



















THE STARRETT BOOK 

for 

MOTOR MACHINISTS 
and AUTO REPAIR MEN 


Volume III of The Starrett Books 


PRICE 75 CENTS 


THE L. S. STARRETT COMPANY 

\ 

World's Greatest Toolmakers 

ATHOL, MASSACHUSETTS 




Copyright 1924 

The L. S. Starrett Company 


2y- Z9TJ6, 


SEP -5 1^24 


©C1AS00C98 

H« j 




PREFACE 

In presenting Volume III of The Starrett Books it has been our 
aim to provide information for the Motor Machinist and Auto 
Repair Man that is comparable with that offered to the Apprentice 
and Journeyman Machinist by Volumes I and II. 

In its preparation we have made no attempt to deal with specific 
motor troubles or the peculiarities of particular makes or models of 
cars, nor have we included any shop “kinks", hints on “trouble 
shooting”, etc. On the contrary, we have confined the text of 
Volume III.to such subjects as would aid the man in the service 
station or repair shop in gaining a better understanding of the uses, 
methods of operation and the value of machine and precision tools. 

While individual credit has been given wherever possible, a very 
large portion of the text of the book represents the combined opinions 
and experiences of a considerable number of men, each of whom is an 
authority in his field. This being the case, a blanket acknowledg¬ 
ment of our indebtedness to the publishers of the various automobile 
papers, to their editorial staffs, and to the contributors to their 
columns, appears to be the only practical solution. We especially 
wish, however, to express our appreciation of the assistance so 
generously given by American Automobile Digest, Automotive 
Industries, Automotive Merchandising, Motor Service, Motor Age 
and Motor World. 


THE L. S. STARRETT CO 
Athol, Mass. 


This is, in a sense, a companion volume to 
Volumes I and II of The Starrett Books — The 
Starrett Book for Machinists’ Apprentices and 
The Starrett Data Book for Machinists —digests 
of which will be found at the end of this book. 


THE STARRETT BOOK 

FOR MOTOR MACHINISTS 


MEASURING TOOLS* 

In the automobile shop all measurements required, with 
a few exceptions, are lineal or length. In some few cases 
it is necessary to know or ascertain area, which is length 
multiplied by breadth, while in still fewer instances volume 
must be figured, which is length times breadth times height. 
As all these measurements are primarily secured by multi¬ 
plying distances, the actual shop methods of measuring 
distances—the precision tools used—are extremely important. 

In the United States, automobile measurements are all 
in inches. Wheelbases, tire sizes, cylinder diameters, shaft 
diameters, etc., are all expressed as so many inches and 
fractions or decimals of an inch. The foot and the yard 
are not used. The standard inch is one thirty-sixth of the 
standard British yard. The United States government owns 
two exact copies of the British standard yard, these copies 
being made of “invar” metal which has a minimum of ex¬ 
pansion and contraction under atmospheric temperature 
changes. The L. S. Starrett Company has, in turn, exact 
copies of the United States copies so that very exact instru¬ 
ments can be constructed to measure down to one ten-thou¬ 
sandth part of an inch. To illustrate what a very tiny dis¬ 
tance .0001 is, it is only necessary to know that a safety 
razor blade is .006 in. thick, paper commonly used for print¬ 
ing books is about .002 in. and a human hair varies from 
.002 to .005 in. 

In France and in many parts of Europe, the unit of meas¬ 
urement is the meter, which is 39.37 U. S. or British standard 

♦See also pp. 13-28, Vol. I, Starrett Books, and pp. 159-168, Vol. II, Starrett 
Books. 

5 



THE 


STARRETT 


BOOK 



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Fig. 2 Toolmaker’s Calipers Fig. 3—Micrometer Depth Gage 

6 



























FOR MOTOR MACHINISTS 


inches in length. The sub-divisions of the meter are the 
centimeter which is 1/100 of a meter and the millimeter 
which is 1/10 of a centimeter.* The only automobiles using 
metric measurements in the United States are those imported 
from other countries. There are, however, some American- 
made cars using metric threads on spark plugs. 

Most automobile parts are manufactured to very exact 
sizes. In some cases the parts must be within .0005 in. of 
the correct size. Piston pins, pistons, cylinders, valves, king 
pins, crankshafts and camshafts are generally made to 
within .001 or .002 in. tolerance. 

Anti-friction bearings, both ball and roller types, are often 
finished to within .0005 in. or half a thousandth of an inch.t 

It can be seen, therefore, that good automobile work 
requires 'working to very close limits, much closer, in fact, 
than in the general run of machine shop practice. Dial 
gages and micrometers form an important part of modern 
shop equipment and the shop mechanic should know how 
to operate these as well as inside and outside calipers, pro¬ 
tractors, straight edges, steel squares, dividers, steel rules, 
surface plates, surface gages, center punches, scribers and 
slide calipers and other precision tools. 

FLAT WORK 

In general, the worker on flat work will need to be pro¬ 
vided with steel rules, dividers, protractors, straight edges, 
steel squares, surface, height, depth and thickness gages, 
center punches, parallels, slide calipers, etc. 

ROUND WORK 

For round work the measurements are by contact, and 
the usual tools are those having contact points. Contact 
measurements are made in two ways: (a) The contact tool 

♦For conversion of millimeters into decimals of an inch see p. 161, Vol. II, 
Starrett Books. , T ^ . 

fFor further information on tolerances see pp. 32-33, Vol. I, Starrett Books, 
and pp. 16-17 and 152, 153 and 154, Vol. II, Starrett Books. 

7 



THE 


STARRETT 


ROOK 


is first set to some standard of length, as, for example, a 
steel rule, or a standard gage. The “set” dimension may 
then be used as a standard for testing the work, (b) The 
reverse of this method may be used for determining sizes, 
viz.: by first setting the contact points to the surfaces of the 
work, afterward using the steel rule or standard gage to 
read the size. 

“FEEL” 


The accuracy of all con¬ 
tact measurements is de¬ 
pendent upon the sense of 
touch (feel). In the case 
of skilled workmen, as for 
example toolmakers, the 
sense of touch is highly de¬ 
veloped. Using suitable 
contact measuring tools, the 
skilled mechanic can readily 
“feel” the difference in 
contact made by changes 
of dimensions as small as 
.00025 in. 

In the human hand the 
sense of touch is most 
prominent in the finger¬ 
tips. Therefore, the contact 
measuring tool should be held by the fingers only, and in 
such a way as to bring it in contact with the finger-tips. If 
the tool is harshly grasped by the fingers, the sense of touch 
or “feel” is much reduced. For this reason the tool should 
be delicately and lightly held instead of gripped tightly. 

While it is possible to transfer by “feel” a length with an 
error not exceeding one-quarter of one-thousandth inch, the 
results are not always easily read. In fact, the personal 
equation is so great that most mechanics prefer to use direct- 
reading tools for all accurate contact work. 

8 



Fig. 4—Calipering Round Work 
on Lathe 








FOR MOTOR MACHINISTS 


To illustrate, a “fit” which an apprentice—depending on 
“feel” alone—would declare perfect, would be instantly re¬ 
jected by an experienced machinist using the same method 
of testing and would be shown to be considerably “out” if 
checked with proper precision measuring tools. Again, the 
question of “feel” plays a great part in determining the accu¬ 
racy of work even when precision tools are used. Scarcely 
any two men will “set” a micrometer or a pair of calipers 
exactly the same on a piece of work. A comparatively inex¬ 
perienced man is apt to literally jam the spindle of a “mike” 
on the work—or else go to the other extreme and not get 
sufficient contact—simply because his sense of “feel” is not 
sufficiently developed. An experienced man—having a good 
sense of “feel”—doing the same work and using micrometers 
measuring by thousandths of an inch, will turn out work in 
which the actual variance is less than a ten-thousandth of an 
inch. The more common tools for contact measurements are 
inside and outside calipers, used in conjunction with steel 
rules, plug and ring gages, and dimension blocks. These, 
however, are not direct-reading tools. The direct reading 
tools in common use are the caliper square and the micro¬ 
meter caliper. 

CALIPER SQUARES 

Caliper Squares—and in this type are included Slide Cali¬ 
pers, Slide Rule Calipers and Circumference Gages, Micro¬ 
meter Caliper Squares, Vernier Calipers and Vernier Height 
Gages—are fundamentally combinations of contact points 
and graduated steel rules. In all of these tools one contact 
is generally fixed and the other adjustable. When in use 
the fixed contact is placed against one surface of the object 
to be measured and the adjustable contact brought up against 
the other surface. The distance between the contact points 
may be read direct from the scale on the beam of the tool. 
Caliper Squares, Slide Calipers and Micrometer Caliper 
Squares are not commonly used in Automobile repair work, 
their place being taken by the Micrometer Caliper, which 

9 



THE 


STARRETT 


BOOK 



is both more accurate and more convenient. The use of 
the Vernier Caliper and Vernier Height and Depth Gages 
is most commonly restricted to the more difficult machine 
tool operations, though many expert machinists, employed 
in automobile repair work, find them great savers of time as 
well as productive of more accurate work. 

VERNIER CALIPERS 


The Vernier Caliper is a refinement of the Caliper Square 
and permits the taking of measurements in thousandths 
of an inch. Apart from the Vernier attachment — the 
construction and use of which is explained in a later para¬ 
graph—the Vernier Caliper is substantially the same as a 
Micrometer Caliper Square and is used in the same manner. 



Fig. 6—Vernier Caliper 
10 




































FOR MOTOR MACHINISTS 


VERNIER HEIGHT GAGE 

Another adaptation of the vernier is the height gage. 
By means of the vernier it is easy to make readings as minute 
as one-thousandth part of an inch. This instrument is used 
chiefly where close, accurate 
measurements of height must 
be obtained. 

By means of suitable adjust¬ 
ments, one of which is shown 
on the accompanying illustration 
(C attachment), its use is ex¬ 
tended to include making accu¬ 
rate measurements of depth. 

MICROMETER 
CALIPERS 

The limit of accuracy ob¬ 
tained by measuring between 
contacts depends on the gradu¬ 
ations on the instrument. It 
is evident that as the fineness 
of the graduation increases, 
the chances for mistaking one 
graduation for another also 
increase so that some other 
method of determining ex¬ 
tremely accurate measurements 
must be used. 

Today, the common instru¬ 
ment for making measurements 
finer than 1/100 of an inch is p IG 7—Vernier Height Gage 
the micrometer caliper. This 

tool combines the double contact of the slide calipers with 
a micrometer screw adjustment which may be read with 
great accuracy, as may be understood when it is realized 
that threaded spindles with a limit of error of .001 in. in 

11 




























BOOK 


THE STARRETT 



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Fig. 8—Phantom View of Fig. 9—Outside Micrometer 
Outside Micrometer 


12 

































































































































FOR MOTOR MACHINISTS 


one-foot lengths are commercially possible. In micrometer 
construction, where used length of screw thread is only 
one inch, the degree of error is negligible. 

A micrometer head consists of a spindle, forty threads 
to the inch, fitted through a threaded sleeve, having an 
enclosing thimble fastened to its outer end. Suitable gradu¬ 
ations made axially on the adjustable sleeve, combined with 
the graduations on the edge of the rotating thimble, give 
direct readings of one-thousandth part of one inch. By using 
a vernier scale on the sleeve, direct contact readings as small 
as one ten-thousandth part of one inch can be readily made. 



Fig. 10—Parts op a Micrometer 


Micrometer screws are mounted in a frame which may be 
varied in shape and size according to the type of work on which 
the tool is to be used. The contact points are also shaped to 
the particular use for which the tool is designed. In general, 
however, micrometer points are ground and lapped parallel 
to each other. Micrometers for either inside or outside 
measurements are purchasable in a variety of styles and of 
the highest degree of accuracy, convenience and finish. 

HOW TO READ A MICROMETER 

The pitch of the screw thread on the concealed part of 
the spindle C (See Fig. 10) is forty to an inch. One complete 

13 









THE 


STARRETT 


BOOK 


revolution of the spindle, therefore, moves it lengthwise one- 
fortieth (or twenty-five thousandths) of an inch. The sleeve 
D is marked with forty lines to the inch, corresponding to 
the number of threads on the spindle. Each vertical line 
indicates a distance of one-fortieth of an inch. Every fourth 
line is made longer than the others, and is numbered 0, 1, 2, 
3, etc. Each numbered line indicates a distance of four times 
one-fortieth of an inch, or one-tenth. 

The beveled edge of the thimble E is marked in twenty- 
five divisions, and every fifth line is numbered from 0 to 25. 
Rotating the thimble from one of these marks to the next, 
moves the spindle longitudinally one twenty-fifth of twenty- 
five thousandths, or one-thousandth of an inch. Rotating 
it two divisions indicates two-thousandths, etc. Twenty- 
five divisions will indicate a complete revolution, .025 or 
one-fortieth of an inch. 

To read the micrometer, therefore, multiply the number of 
vertical divisions visible on the sleeve by twenty-five, and 
add the number of divisions on the bevel of the thimble, 
from 0 to the line which coincides with the horizontal line 
on the sleeve. For example, in the engraving, there are 
seven divisions visible on the sleeve. Multiply this num¬ 
ber by twenty-five, and add the number of divisions shown 
on the bevel of the thimble, 3. The micrometer is open one 
hundred and seventy-eight thousandths. (7 x 25 equals 175 
and 175 plus 3 equals 178.) 

HOW TO READ A VERNIER 

Readings in thousandths and ten-thousandths of an inch on 
caliper squares, micrometers, etc., are obtained by the use 
of a Vernier, named after a Frenchman, Pierre Vernier, who 
invented the device in 1631. For the Vernier caliper, the 
scale on the tool is graduated in fortieths of an inch (.025). 
On the Vernier plate (See Fig. 11) is a distance divided into 
twenty-five parts, and these twenty-five divisions occupy 
the same distance as twenty-four divisions on the scale. 

14 



FOR M 0 T 0 R M A CHINISTS 


The difference between one of the twenty-five spaces and 
one of the twenty-four spaces is one twenty-fifth of one- 
fortieth, or one-thousandth of an inch. 

To read the tool, note how many inches, tenths (or .100), 
and fortieths (or .025) the 0 mark on the Vernier is from 
the 0 mark on the scale; then note the number of divisions 
on the Vernier from 0 to a line which exactly coincides with 
a line on the scale. 



In Fig. 11, the Vernier has been moved to the right one 
and four-tenths and one-fortieth inches (1.425 in.), as shown 
on the scale, and the eleventh line on the Vernier coincides 
with a line on the scale. Eleven-thousandths of an inch are, 
therefore, to be added to the reading on the scale, and the 
total reading is one and four hundred and thirty-six thou¬ 
sandths inches (1.436 in.), which is the distance the jaws 
have been opened. Because of the extreme accuracy re¬ 
quired in most work on which a Vernier is used, many skilled 
machinists employ an eyeglass when reading the scale. By 
so doing, the possibility of error is greatly reduced. 

15 

















THE 


STARRETT 


BOOK 


HOW TO READ 
A VERNIER MICROMETER 

Readings in ten-thousandths of an inch are obtained on 
the Micrometer by the use of a Vernier, which operates on 
the same principle as the Vernier on the caliper. In this 
case, however, ten divisions on the sleeve occupy the dis¬ 
tance of nine divisions on the thimble. The difference be¬ 
tween the width of one of the ten spaces and one of the nine 
spaces is one-tenth of a division on the thimble. 

Each division on the thimble represents one-thousandth 
of an inch, and one-tenth of one-thousandth equals one 
ten-thousandth. To read a ten-thousandth micrometer, first 
note the thousandths as in the ordinary micrometer. Then 
observe the line on the sleeve which coincides with a line 



Fig. 12—Vernier Micrometer Scale 


on the thimble. In Fig. 12 there are nine vertical divisions 
visible on the sleeve, and 9 x 25 equals 225, so that the 
reading of the ordinary micrometer would be .225. Line 
marked “7” on the sleeve coincides with a line on the thimble 
and, therefore, we add seven to the reading of the ordinary 
micrometer. This seven is seven ten-thousandths (.0007), 
and the reading will be .2257. 

16 











































FOR MOTOR MACHINISTS 


OPERATION AND ADJUSTMENT OF 
MICROMETERS 

QUICK MEASUREMENTS.—Some micrometers have 
a quick-adjustment feature and can be instantly opened or 
closed to any size within the capacity of the tool. On such 
tools, pressure of the finger on the end of the plunger allows 
the spindle to move instantly to approximately the desired 
size without turning the thimble. When the finger is 
removed, fine adjustments may be made in the usual way. 

MICROMETER AS A GAGE.—Most micrometers have 
a knurled lock nut, by means of which the spindle can be 
firmly fixed in position, making the micrometer a solid gage. 
While this is common practice, the tool should not be used 



for this purpose. Instead, gages made expressly for such 
work and known variously as “go and not go”, “snap” and 
“limit” gages, should be employed. In one type of micro¬ 
meter, turning the lock nut contracts a split bushing around 
the spindle, keeping it central and true, while in others, a 
cam principle is used, the ring and lock nut being set in the 
frame. 

READJUSTMENT FOR WEAR.—When slight wear 
makes correction necessary, the readjustment is accomplished 

17 




THE 


STARRETT 


BOOK 


by various means and degrees of ease and accuracy, accord¬ 
ing to the make of micrometer. With the Starrett micro¬ 
meter the anvil is fixed, not movable, and correction is 
quickly made by inserting a spanner wrench in the friction 
sleeve under the thimble and turning until the line on the 
sleeve coincides with the zero on the thimble when the 
micrometer is closed or is against a standard plug (See 
Fig. 13). This adjustment feature does away with all need 
for the frequent use of a test piece. 



Fig. 14—Inside Micrometer (Starrett) 


INSIDE MICROMETERS 

In addition to outside measurements with micrometers, 
automobile work requires the very exact measurements of 
inside diameters such as cylinder bores, etc. Inside micro- 

18 













































FOR MOTOR MAC H I N I S T S 


meters are instruments employing the micrometer principle 
in such a way that inside diameters can be taken. An inside 
micrometer may be used to determine whether cylinders have 
worn oval or have become tapered from top to bottom, 
though the Starrett Cylinder Gage is far preferable for this 
particular sort of work. 



Fig. 15 —Measuring a Cylinder Bore with Inside Micrometers 


The micrometer screw in the head of the inside micrometer 
shown in Fig. 14, has half inch movement, and by means of the 
extension rods measures bores from 2 to 32 inches in diam¬ 
eter by thousandths of an inch. The extension rods are 
provided with a collar against which the rods are conven¬ 
iently and accurately set in the micrometer head. In set- 

19 



































THE STAR RETT BOOK 


ting, care must be taken to see that the zero mark on the 
collar coincides with the zero mark on the micrometer head. 

Micrometers are made in a wide range of sizes, styles and 
purposes. Starrett micrometers are made to read in either 
English or Metric measure, reading in English measure in 
thousandths or ten-thousandths of an inch and with a range 
in size—capacity—from 0 in. to 24 in., and in Metric 
measure in millimeters, the range being from 0 to 150 m.m. 



Fig. 16 —Dial Gage (Starrett) 


DIAL GAGES 

Primarily, dial gages are not instruments for making meas¬ 
urements as they do not ordinarily directly indicate distance. 
They do, however, indicate differences in sizes within their 
range. In combination with a micrometer, however, they 
can be used to measure exact distance. The dial gage is a 
great help in testing shafts for alignment, for testing cylinder 
20 




















FOR MOTOR MACHINISTS 



Fig. 17 —Applications of Dial Test Indicator 
21 








































THE 


STARRETT 


BOOK 


DECIMAL EQUIVALENTS OF FRACTIONS OF AN INCH* 


% 

.5 

3 % .515625 
.53125 
% .546875 

% 

.5625 


% .578125 

% 

.59375 


3% .609375 

% 

.625 


% .640625 


.65625 


% .671875 

% 

.6875 


4 % .703125 

% 

.71875 


% .734375 

Z A 

.75 


4 %i .765625 

2 % 

.78125 


% .796875 

% 

.8125 


5 % .828125 

% 

.84375 


% .859375 

Vs 

.875 


% .890625 

% 

.90625 


% .921875 

% 

.9375 


H2 


hi. 


16 


H 


H 


.015625 
.03125 
% .046875 
.0625 
.078125 




.09375 
% .109375 
.125 
.140625 
.15625 


% .171875 
.1875 
.203125 
.21875 
15 { 4 • 234375 


32 


.25 

17 4 .265625 
.28125 
.296875 
.3125 


19 4 


% .328125 
% -34375 

% .359375 
.375 

25 4 .390625 


% 


% 


.40625 
.421875 
.4375 

T64 .453125 
.46875 
3 % .484375 


29/, 


-953125 
.96875 
6 % .984375 


•For other decimal equivalents, tables of weights and measures, squares, cubes 
and square and cube roots, etc., see pp. 165-169, Vol. II, Starrett Books. 

22 

















WRENCH SIZES FOR BOLTS, NUTS AND CAP SCREWS 






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*Wrench sizes for S. A. E. standard spark plugs. 

Note: Wrench openings are milled 1/64 in. above the nominal wrench opening 
given in the first column up to 1 V4 in. Above this size the clearance is 1/32 in. 
or even more in the still larger sizes. Set screws take the same size opening as 
the diameter of the screw. 

23 





















THE 


STARRETT 


BOOK 


bores for roundness and taper and for testing bearing bores. 
In any of these jobs, the dial gage indicates directly to within 
.001 in. the alignment or roundness of the article being 
tested. In the hands of a skilled man, the instrument can 
be read to within .00025 in. The dial gage is extensively 
used in manufacturing and is rapidly being found a neces¬ 
sity in service and repair work. 

Dial Test Indicators may be used to advantage in con¬ 
nection with straightening crankshafts, locating wrist pin 
holes, determining amount of shim to insert or remove, 
determining taper, checking play in bearings, reboring work, 
lining up Ford Magneto Coil Assembly, etc. 

FILING* 

The file, one of the most common tools in the shop, is a 
cutting tool with a great number of fine, sharp edges or teeth 
which do the cutting when the file is moved forward across 
the work. Files are made in a great variety of shapes, sizes 
and tooth grades to meet various requirements. 

The more common shapes are hand, flat, mill, round, half 
round, square, pillar, three square, taper and slim taper. 
The lengths range from 3 in. to 20 in. or more. The follow¬ 
ing would be a typical selection for an automobile shop: 

Hand bastard, 8, 10 and 12 in. 

Flat bastard, 8, 10 and 12 in. 

Flat smooth, 10 and 12 in. 

Half round second cut, 6, 8 and 10 in. 

Mill second cut, 8 and 10 in. 

Square second cut, 6, 8 and 10 in. 

Taper second cut, 3, 4, 6 and 7 in. 

Round second cut, 3, 4, 6 and 8 in. 

Hand rough, 10 and 12 in. 

The size of the teeth or cut starts with the coarsest to the 
finest, rough, bastard, second cut, smooth and dead smooth. 
The relative sizes of the teeth are shown in the illustration. 

*See also pp. 40-42, Vol. I, Starrett Books. 

24 



FOR MOTOR MACHINISTS 



Pillar 



Warding or Taper 



Round 





Half Round 




Three Square 



Flat 



Mill 

Fig. 18—File Shapes 

25 














































THE 


STARRETT 


ROOK 




































FOR MOTOR MACHINISTS 


The teeth vary in the same cut with the size of the file, a 
bastard cut being larger in a 10 in. file than in a 6 in. file. 

Most of the cuts are to be had in either single or double 
cut. A single cut file has the teeth cut across in one direc¬ 
tion only. Double cut files have the teeth cut in two direc¬ 
tions across the file, the cuts being at a considerable angle 



Fig. 20—Parts of a File 

to each other. Double cut files are to be preferred for all 
general shop work as they do better work and last longer. 
The single cut files are useful for finishing up fine work and 
for draw filing. 

The length of a file is from the heel to the point, exclu¬ 
sive of the tang. The point is the end farthest from the tang 
and the heel is the juncture of the tang and the file proper. 
Some files have one or more edges or sides without teeth. 
These are known as “safe” sides or edges and are useful in 
fitting step joint piston rings, etc. 

Files are made of high grade carbon steel, hardened and 
tempered. In the hardening process it is quite common for 
the file to attain a very slight curvature which can be used 
to advantage when the mechanic wants to file perfectly flat 
or slightly hollow. Sighting along the file will tell how any 
particular file is curved and which side to use. 

Much better work can be done with a file if it is properly 
handled. Patent iron or steel handles with quick acting 
fastenings are fast finding favor. Wooden handles should 
be in proportion to the size of the file. The handle should 
be put on straight and the tang should go into the 
handle almost up to the heel. To avoid splitting the handle, 
heat the tang of an old file of the same size to a red heat and 
drive the handle on, the tang burning its way in. When 

27 






THE 


STARRETT 


ROOK 


nearly to the desired point, the handle is pulled off, and the 
new file, first having been dipped in water, is driven on tight. 
A file handled this way will stay handled. 



The proper height for filing depends on the height of the 
mechanic. When he stands straight and in a filing position, 
if the right forearm and file are in a straight line the position 
is about perfect. For the average man this height is about 

28 






















FOR MOTOR MACHINISTS 


42 in. If the mechanic is short he should use a wooden 
platform to bring his elbow to the height of the work. 

Files will last longer and give better service if they are 
properly taken care of. Being highly tempered, the teeth 
are quite brittle and, therefore, files should never be thrown 
around on a concrete floor nor thrown one on top of the 
other. It is preferable that there be racks to hang them up 
when not in. use. This will also keep them out of oil and 
grease which are bad for files and prevent their cutting, 
although oily files can be cleaned with gasoline. It is better 
to use a file exclusively on one metal. Files for brass might 
have red handles, for iron and steel black handles and for 
babbitt and lead, varnished or natural handles. 

When files become clogged with bits of metal, they will 
scratch and they should be cleaned with a file card which is 
a sort of wire brush with tiny bent wires. A file which 
screeches can be silenced by rubbing chalk in it. In finish 
filing the use of chalk or oil will eliminate “bugs”. Use old, 
worn out files for lead and babbitt as these metals will clog 
up a sharp file. Worn out files can be recut, but unless they 
are large and expensive the cost of recutting is hardly worth 
while. The teeth of an old file can be sharpened slightly 
by first removing all oil or grease from the file with gasoline 
and then soaking it for four to eight hours in dilute sulphuric 
acid. The teeth, however, while somewhat sharper will not 
be exactly even. 

HOW TO USE HACK SAWS* 

The hack saw is one of the essential tools of the auto¬ 
mobile shop. It is used to cut a great variety of metals and 
other substances and in many shapes. Here are some of the 
jobs ordinarily encountered: Sawing out rusted bolts and 
studs; cutting old bronze bushings, new bolts, drill rod, etc.; 
sawing off brass and copper gasoline and oil pipes; cutting 
screwdriver slots in cap screw heads; sawing through chassis 

♦See also “Hacksaws and Their Use,” The L. S. Starrett Co., publishers. Also 
pp. 43-46, Vol. I, Starrett Books, and pp. 103-106, Vol. II, Starrett Books. 

29 



THE 


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ROOK 


frames for extensions and through old solid rubber tires and 
rims for removal; undercutting commutator mica; sawing 
fiber sheets and blocks for electrical work; removing and 
replacing piston rings; sawing lead battery connectors and 
posts; sawing slots in exhaust pipes for cut-outs and car 
heaters; sawing cast iron pistons for cylinder laps. 




Fig. 22—Hacksaw Frames (Starrett) 


Practically all of this work is done with hacksaws used in 
a hand frame with blades 8, 10 or 12 in. long. In the larger 
shops where a considerable quantity of sawing is done it 
will pay to use a power hacksaw. This is especially true 
where the shop does assembling, partial manufacturing, body 
building, etc. 

The life of a hacksaw practically ends when a tooth breaks. 
After the first tooth goes, an additional strain is placed on 
the tooth in back of the broken one and it is only a matter 
of a short time until a number of teeth are missing and the 
saw ruined as a cutting tool. While hacksaw blades are 
comparatively cheap, much money can be saved by using 
the saws to best advantage and prolonging their life as much 

30 












FOR MOTOR MACHINISTS 


as possible. Using the proper blade in the proper manner 
will increase the life of the saw several hundred per cent and 
save an incalculable amount of time and effort.* 

Hacksaw frames should be stiff and rigid so that there is 
no frame weave or movement on either the forward or back 
strokes. If of the extension type, there should be no bowing 
of the frame’s back when tension is placed on the blade. 
The handle should fit the user’s hand comfortably and— 
unless of the regulation “saw-handle” or “easy” type— 
should be straight with the rest of the frame. The pins 
which hold the blade in place should be in tight and should 
have enough rake to keep the saw from slipping off. Hack¬ 
saw blades should always be so placed in the frame that the 
rake of the teeth is forward—that is, away from the operator. 

Before using, the saw should be strained or tightened so 
that it gives a sort of musical twang when plucked like a 
fiddle string. A loose saw will break easily. A saw too 


:: , • • STAHR^TT-"*" •* * 


Fig. 23— Hacksaw Blades (Starrett) 


tight is liable to break the blade. Looseness in the blade 
often causes a slight twist in the cut. 

Too much care cannot be exercised in the choice of the 
saw used. Different materials and different shapes require 
blades of varying thickness or gage, as well as a varying 
number of teeth to the inch. To insure the economical, 
efficient use of hacksaws consult the Starrett Hacksaw Chart 
for Automobile Shops (Page 33). 

When using hacksaws be sure to put sufficient pressure on 
the saw to make the teeth cut. If the saw lazes across the 


•See page 33. 

Note: For information as to the proper blades to use in ordinary machine shop 
work see the regular or Standard Starrett Hacksaw Chart, Vol. II, Starrett Books. 


31 





THE 


STARRETT 


BOOK 



Fig. 25—Hacksaw Blades Used to Remove Piston Rings 

work without cutting, the teeth are dulled rapidly, shorten¬ 
ing the life of the blade. Where practical, release the pres¬ 
sure on the back stroke. Make the stroke as near the full 
length of the blade as possible. Do not attempt to cut 
through hardened or tempered steel and go cautiously on 
welded iron or steel work. The rapid chilling of the "weld 
often makes the metal nearly glass hard. When cutting a 
weld or tempered steel is unavoidable, the metal should— 
whenever possible—first be heated to a cherry red and cooled 
slowly, the work being handled as in annealing and the metal 
not allowed to cool in air. 


32 




















FOR MOTOR M A C H I N I S T S 


STARRETT HACKSAW RECOMMENDATIONS 
FOR AUTOMOBILE WORK 


1 . 


Sawing out rusted bolts and studs, ^ 
diameters from }4 to % in., cold [ 
rolled steel, nickel steel and f 
molybdenum steel. J 


No. 250 and No. 250-B 


2. Sawing out worn bronze bushings. No. 250-B 

3. Sawing new bolts, studs, drill rod, j No . 25q and Nq _ 2g0 _ B 


4. Sawing brass and copper gasoline 

and oil pipes, diameters inside 34 
and P{q. Thickness about 34 to 
Annealed. 

5. Sawing screw driver slots in cap’ 

screw heads, cold rolled and nickel 
steel. 


No. 252 and (No. 258 for 
under }{$" thick) 


No. 115 and No. 249-A- 
B-C-D 


6. Sawing through chassis frames for \ oc - n n om r> 

extensions, patching, etc.*.) No. 250 and No. 250-B 

7. Sawing through old solid rubber v 

tires and steel rims for removing 1 No. 115 and No. 115-B 
when hydraulic press is not avail- f No. 262 and No. 259 
able. ' 


8. Undercutting commutator mica. ... No. 103-No. 112 

9. Sawing fiber sheets and blocks fori No. 103-No. 112. All 

electrical work./ hard saws 32 to 18 point. 

10. Sawing lead battery connectors and n 

posts. Metal is about 98 per cent l 

lead with a little antimony for j No. 250-B 

hardness.' 

11. Sawing slots in exhaust pipes for in- N 

stalling cut-outs and car heaters. 

The pipes are from 134 to 3 in. out¬ 
side diameter and from^g to 34 in. 
thick. The slots are usually 
sawed V-shape about halfway 
through the pipe. In some cases 
the cut is square with the pipe, a 
diagonal being sawed and the flaps 
bent out and cut off. 

12. Sawing through cast iron pistons to \ 

make cylinder laps. J No. 250-No. 115-No. 262 

♦Note: No. 6 is same as No. 1 and applies if the frames are of molybdenum steel. 

33 


No. 258 for 34" thick 
„ No. 252 for%>" thick 
No. 250 for 34" thick 












THE 


STARRETT 


ROOK 


Old hacksaw blades may be saved and the teeth ground 
off so that they can be used behind piston rings for remov¬ 
ing and installing. 

REAMERS AND REAMING* 

There are two general classes or divisions of reamers; 
those employed in only the rougher kinds of work, and 
those used in the production and repair of high grade machin¬ 
ery. Hand reamers, such as are used in automobile service 
station and repair shop work, belong in the second class and 
are really high grade precision tools. 



Fig. 26—Reamer 

There are three types of hand reamers which have come 
to be generally accepted by mechanics and machinists as 
standard. The first is the straight, solid, fluted reamer with 
regularly spaced flutes (See Fig. 26 ). 

This is the oldest and is still the most common type of 
reamer in general machine shop practice, although in auto¬ 
mobile repair work reamers of the expanding type have 
largely displaced it. The solid reamer is a rugged tool, 
made from a single piece of steel in which are cut longitudinal 
grooves or flutes providing the necessary high sections or 
“lands”. These “lands”, or cutting edges, are hardened, 
tempered and carefully ground to very close limits. For 
accurate work this type of reamer cannot be excelled, but 
its rapid loss of size through wear and its lack of flexibility 
places it at a disadvantage and accounts for the popularity 
of expansion or adjustable type reamers. The solid reamer, 
while originally made with straight, regularly spaced flutes, 
is now often found with irregularly spaced flutes to avoid 

*See page 98, Vol. I, Starrett Books, and pp. 99-101, and 114-121, Vol. II, 
Starrett Books. 


34 












FOR MOTOR MACHINISTS 



Fig. 27 



Fig. 28 



Fig. 29 



Fig. 30 



Fig. 31 



Fig. 32 



Fig. 33 



Fig. 34 

35 
















































































THE 


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ROOK 


“chatter”, which will cause a roughness in the finish of the 
work, and is also made in spiral form as shown in Fig. 27. 
This tool is often used to advantage when reaming bearings 
having an oil groove or other open space. 

The expansion reamer (See Fig. 28), as its name indicates, 
is a semi-solid tool so made that it may be expanded a few 
thousandths of an inch by means of a taper screw plug. This 
permits compensation for a limited amount of regrinding. 
The tool, however, does not give the extreme accuracy of the 
solid reamer. 

The adjustable reamer, often called the Critchley Type 
reamer (Fig. 30), is entirely different in principle and con¬ 
struction from the types already described. In this type 
the blades are separate from the body of the tool and are 
mounted in staggered grooves taper milled in the shank of 
the tool, which is threaded to take adjusting nuts that serve 
to move the blades up or down the grooves, increasing or 
decreasing the diameter of the reamer. The great flexibility 
of the tool, coupled w T ith the fact that the blades may be 
repeatedly reground or replaced when necessary, has won for 
it great popularity with the motor machinist and auto repair 
man. Its disadvantages are that its construction is such that 
the tool is easily injured. It must be kept clean and requires 
great care in its use if anything approaching accurate work is to 
be done. 

All these types of reamers—the solid, expansion and adjust¬ 
able, or Critchley—are also manufactured with pilots to assist 
in guiding the reamer in various kinds of work, especially 
where it is necessary to ream two or more bushings or bearings 
in perfect alignment. Among reamers equipped with pilots are 
the solid reamer with starting and aligning pilots, the crank¬ 
shaft bearing reamer (Fig. 31), the spiral reamer with starting 
and aligning pilots (Fig. 32), the spindle bolt bushing reamer 
with short flutes and rear pilot (Fig. 33) and expansion reamers 
with front and rear pilots (Fig. 34). 

In general machine shop practice a reamer is ordinarily used 
to finish a hole true to size after first boring it with a drill 

36 



FOR MOT OR MACHINISTS 


or with a boring bar on a lathe or some other machine tool. 
Often an arbor, or mandrel, will be forced into this hole 
and other, surfaces finished on the lathe, using the centers 
which are in the arbor. This is a very common job to lathe 
workers and is pretty well understood by machinists. In 
automobile work, however, it is seldom that this sort of work 
is performed excepting in cases of emergency where a special 
part has to be made to order. 

Practically all parts supplied by manufacturers through 
distributors, dealers and agents fit into the car or the unit 
without further machine work or fitting, with the exception 
of bearings and bushings. These latter have to be fitted 



Fig. 35 

by the mechanic by scraping, reaming or lapping. The pro¬ 
cess used depends on the character of the bearings. 

In the case of bronze bushings, the fitting is done with 
reamers which finish cut the holes in the bushings to an exact 
fit for the pin or shaft, etc., that is to work in the bushing. 
For that reason, it is customary to replace the pin as well 
as the bushing, because they both wear. The rebushed part 
will then have parts that fit in every respect as they did when 
the car was new. 

Where a bronze bushing is by itself and does not have to 
line up with anything else, it is simply driven in place with 
an arbor press and the hole carefully reamed. Spring eye 
bushings would be examples of this kind. 

Where, however, the bronze bushings are in pairs and have 

37 








THE 


STARRETT 


ROOK 


to line up with each other, different methods have to be 
used. Bronze bushings are in pairs in the steering spindles, 
in the pistons, in many cases as bearings for the wrist pins, 
and sometimes in the gear-case. Camshaft and crankshaft 
bushings and bearings also call for alignment in reaming. 

In reaming bearings opposite each other, or paired, a pro¬ 
cess is used which is called align reaming. The type of 
reamer to use on this work has already been described and 
is called an aligning or “align” reamer. The illustrations 
show how an align reamer works and what sort of hole might 
result if an ordinary reamer were used (See Fig. 35). 

Reamers are also used in places other than bearings. 
When valve stems wear loose a reamer a few thousandths of 
an inch oversize is run through the stem hole and a new valve 
with an oversize stem inserted. Where the stem guide is 
removable the old one is pressed out, a new one pressed in 



Fig. 36—Valve Reseater 


and a reamer run through. A valve seat reamer with teeth 
at an angle of 45 degrees—or whatever may be the correct 
valve angle for the particular make of motor, trues up the 
valve seat preparatory to grinding, thus saving considerable 
time and insuring a better seat. This tool is sometimes called 
a valve reseater, but it is really a special reamer. The better 
types have two cutting faces, one of which should be used 
for the roughing cut, removing the glaze from the valve 
seat, the other being reserved for the finish cut (Fig. 36). 

Taper pin reamers are used to ream tapered holes to fit 
standard taper pins. These are often used in such places as 
starting crank pins, pins to hold magneto and generator 
couplings to lay shafts, etc. Standard taper pins and reamers 
have a taper of 34 in. per ft. The numbers run from 0000, 
which is the smallest, to 14, which is the largest. The sizes 

38 





FOR MOTOR MACHINISTS 


of taper pin reamers usually met with in automobile work 
range from 0 to 5 or 6. A table of standard taper pin and 
taper pin reamer sizes is given on page 44. 

USING REAMERS 

All stock reamers of all kinds cut right-handed. That is, 
they turn the same direction as a drill or as a screw when it 
is screwed in. The cutting edge of a reamer is so shaped 
that it has some bearing surface and some clearance. For 
that reason, a reamer should never be turned backward in 
the hole. To do so will impose more wear on it than it 
would receive in reaming a score or more holes. 

Reamers are made from good quality tool steel tempered 
fairly hard. They, therefore, must be handled carefully, not 
dropped or thrown and never laid or dropped against other 
tools or reamers. To do so is to run a chance of nicking the 
sharp edges. Expansion reamers are often broken by try¬ 
ing to force them beyond their normal range of expansion 
and by expanding them rapidly. Adjustable or Critchley 
Type reamers must be kept clean in order to work properly 
or even satisfactorily. Their design is such that dirt, chips, 
etc., often work underneath the cutter blades, forcing the 
reamer out of true, causing chattering, digging in, etc. 
Broken blades, twisted shanks and poor, inaccurate reaming 
are often the result of dirt on the tool. Critchley Type 
reamers should be washed with gasoline after use and should 
be taken apart and properly cleaned. Care must be taken 
to see that each blade is replaced in the slot from which it 
was removed. 

Reamers should not be expected to take out too much 
metal at a single cut. For sizes from 34 to 1 in. the usual 
allowance is about .003 to .005 in. For sizes larger than 
1 in., the allowance is generally a little more. On any job 
calling for the removal of an excessive amount of metal a 
drill or boring bar should be used to take out most of the 
metal before attempting to ream the hole. 

39 



THE 


STARRETT 


ROOK 


Reamers are usually made to feed themselves into the 
work at the proper speed. Feeding them too fast or too 
slow will cause chattering and an uneven hole. Spiral fluted 
reamers feed themselves and straight fluted reamers will 
feed themselves if used vertically. Otherwise a slight pres¬ 
sure should be used. 

The work, when reaming, should be held firmly and in 
such position as is most convenient for the operator. The 
use of a bench vise, where size permits, is recommended or 
in cases where the piece is too large to be handled in this 
manner, the work should be clamped to the face plate of a 
drill press with a lathe center in the spindle to take the 
reamer, which should, however, invariably be turned by 
hand. A hand reamer should never be operated by power. 

Use a tap wrench on a reamer where possible in preference 
to a monkey wrench, solid wrench or pipe wrench. This 
will prolong the life of both reamers and wrenches as well 
as produce better work by distributing the turning force 
on both sides of the reamer so that there is no side pressure. 

Reamers must be started and opera ted with considerable care 
in babbitt as the metal is very soft and even a moderate pres¬ 
sure sideways on the reamer will cause it to cut out of line. 

When a reamer gets dull it can be sharpened by grinding, 
but the grinding of reamers should not be attempted except 
by those who are skilled in the art and have the proper special 
equipment. The reamer manufacturer or his agent will be 
glad to perform this kind of work and guarantee a true job.* 

REAMER SHARPENING 

As has already been stated, reamer sharpening is 
a factory operation and one which calls for a considerable 
amount of special equipment. It is, however, practical for 
the average machinist to restore the edge of a slightly dulled 
reamer by using a thin hone or abrasive wheel in the flutes, 

*For a table of reamer clearances for grinding reamers see Starrett Books 
Vol. II, pages 100,101. 


40 



FOR MOTOR MACHINISTS 

but anything beyond this should be done as closely as pos¬ 
sible along the methods followed by the maker of the reamer. 
In the case of Critchley Type, or adjustable reamers, some 
manufacturers are now making them with interchangeable 
blades. This makes it possible to entirely avoid both the 
use of dull reamers and the uncertain results of attempting 
to grind them in the shop, since all that is necessary is to 
buy a new set of blades—exactly as though the tool was a 
safety razor—drop them into position in the slots in the 
shank of the tool and get on with the work. All makes of 
reamers of the Critchley Type, however, do not possess this 
feature and, of course, new blades cannot be put into either 
the solid or expansion types of reamer. For that reason, in 
view of the delay that factory repairs usually entail, it may 
not be out of place to explain briefly factory methods of 



Fig. 38—Cross Section of Solid Reamer after Rotary Grinding 

reamer sharpening for such repair shops, service stations, 
etc., as have the requisite mechanical equipment. 

In factory practice, reamer grinding is divided into two 
operations; the rotary grinding and the “backing off” or 
relieving. The rotary grinding is a wet process and differs 
in no way from other operations of its kind except that it 
calls for extreme care and accuracy as it is at this stage that 
the size of the reamer is determined. A cross section of a 
solid, fluted reamer after grinding is shown in Fig. 38. 
Note that at this stage the reamer has no cutting quality 
whatsoever. It is not until the individual flutes are backed 
off that the reamer becomes a cutting tool. 

41 




THE 


STARRETT 


ROOK 


Backing off, or relieving, determines the efficiency of the 
tool and is the phase of regrinding in which most machinists 
fail. Relieving is done by placing the reamer on centers in 
a tool grinder and using—ordinarily—a cupped wheel. The 
angle of relief is all-important and is determined by the 
height of the tooth rest with reference to the center of the 
reamer. One blade is ground at a time and is held in posi¬ 
tion by the tooth rest. 

The proper angle of relief ranges between 5° and 10°. In 
automobile repair work 7° will probably be found most satis¬ 
factory. / 



Fig. 39 —Section of Solid Reamer after Grinding Clearance on 
Blade 

When relieving, a narrow section should be left between 
the lip of the blade and the point at which the backing off 
commences. This is known as the “land” and its width 
varies from .005 to .025 in. according to the work on which 
the tool is to be used. Here again a mean will be found 
most satisfactory for automobile repair work and a “land” 
of about .010 is recommended. A cross section of a solid 
reamer backed off in accordance with these recommendations 
is shown in Fig. 39. 

Figure 40 shows the relative positions of the reamer and 
grinding wheel centers when grinding off the cutting edge. 
Note that the wheel center is below the reamer center for 
grinding on the cutting edge to secure greater keenness. 
Generally speaking, it is safer to run the grinding wheel off 
the edge as shown in A, but a keener cutting edge may be 
secured by following the practice indicated in B, although 
there is danger of the wheel action drawing the tool away 
from the tooth rest. 


42 




FOR M 0 T O R MACHINISTS 



Fig. 40—Relative Positions of Reamer and Grinding Wheel 

Centers 

Table of Drills for Reaming 

The drill size is in. less than the reamer size in each case, this 
being the proper amount of stock to leave for reaming under average 
conditions, providing the drill is correctly ground. 


Reamer 

Size 

Drill 

Size 

Reamer 

Size 

Drill 

Size 

Reamer 

Size 

Drill 

Size 

M 


he 


l % 

51 4 

he 


Vs 

*% 

Vs 

S5 4 

Vs 


'he 

4 % 

l he 


he 

27 4 

X 

4 % 

1 


X 

S1 ^i 






STANDARD TAPER PINS AND TAPER PIN REAMERS 
Taper Pins Reamers 


No. 

Diam. at 
Large 
End 

Approxi¬ 

mate 

Fraction 

Diam. at 
Small 
End 

Diam. at 
Large 
End 

Flute 

Length 

Drill 

Size 

No. 

0000 

. 109 

% 

.088 

. 114 

IX 

42 

000 

. 125 

Ys 

.101 

. 130 

IVs 

37 

00 

. 141 

% 

. 114 

. 145 

IX 

32 

0 

. 156 

% 

. 127 

. 161 

IVs 

29 

1 

. 172 

n 4 

. 146 

. 182 

IX 

27 

2 

. 193 

Ye 

. 162 

.204 

2 

21 

3 

.219 

% 

. 183 

.230 

2H 

15 

4 

.250 

M 

.208 

.251 

2 X 

4 

5 

.289 

Hei 

.240 

.303 

3 

X 

6 

.341 

ll hi 

.279 

.355 

SVs 

% 

7 

.409 

13 4 

.331 

.425 

4^ . 

h2 

8 

.492 

y 2 

.398 

.507 

5H 

13 h 2 

9 

.591 

i % 

.482 

.610 

6H 


10 

.706 

4 % 

.581 

.727 

7 

19 hi 

11 

.857 

55 4 

.706 

.878 

8M 

2 h 

12 

1.013 

l l 4 

.842 

1.050 

10 

5 hi 


For tables of dimensions of Morse, Jarno, B. & S., Whitney,etc..standardsockets 
and shanks see pages 114 to 121 of Vol. II, Starrett Books. 

43 





























THE 


STARRETT 


ROOK 


TAPER REAMERS FOR STANDARD TAPER SOCKETS 


MORSE 


No. of 
Taper 

Total 

Lgth. 

Diameter 

Taper, 

Inch 

per 

Foot 

Lgth. 

of 

Flute 

Groove 

Shank 

Diam¬ 

eter 

Square 

Small 

End 

Large 

End 

Depth 

B’t’m. 

Width 

Side 

Lgth. 

0 

3 Vi 

0.250 

3.371 

0. 625 

2'A 

1/40 

At 


A 

As 

1 

5'A 

0.367 

0.367 

0. 600 

3 

1/40 

A 

'At 

2 Ai 

A 

2 

7 

0. 569 

0.517 

0. 602 

3'A 

At 

As 

2 At 

A 

A 

3 

8 

0.775 

0.745 

0. 602 

4 A 


% 

A 

2 At 

' As 

4 

9 

1.017 

0.988 

0. 623 

5 'A 

% 

At 

l'A 

27 A 

l 

5 

10 

1.471 

1. 289 

0. 630 

6M 

V, 

V, 

l'A 

l'A 

1 A 

6 

12 

2. 112 

1.799 

0. 626 

*A 

As 

As 

2 

l'A 

lAs 

7 

16 

2. 746 

2. 555 

0. 625 

12 

As 

Vi 

2Vs 

V'A 

1A 


JARNO 


1 

i 3 A 

0. 100 

0. 1438 

0. 600 

A 

1/40 

A 

Vs 

A 

As 

2 

2 A 

0. 200 

0.2688 

0. 600 

m 

1/40 

At 

l A 

"Ai 

At 

3 

3A 

0.300 

0.4000 

0. 600 

2 

1/40 

At 

Vs 

% 

Vs 

4 

4A 

0.400 

0.5312 

0. 600 

2 A 

1/40 

V* 

'At 

2 A 

'A 

5 

5 A 

0. 500 

0. 6594 

0. 600 

3As 

1/40 

Vi 

'At 

2 A 

Vs 

6 

5 A 

0. 600 

0. 7875 

0. 600 

3 H 

At 

As 

'As 

S A 

Vs 

7 

6 A 

0. 700 

0.9156 

0. 600 

4As 

At 

As 

'As 

*A 

Vi 

8 

m 

0.800 

1.0438 

0. 600 

4 A 

At 

A 

'As 

4 A 

Vs 

9 

8 A 

0.900 

1.1688 

0.600 

5A 

At 

A 

1 As 

5 A 

Vs 

10 

8 A 

1.000 

1.2969 

0. 600 

5'As 

A 

At 

l'A 

2 A 

1 

11 

9 A 

1. 100 

1.4219 

0. 600 

6As 

S A 

At 

lAs 

5 A 

1 

12 

lO'A 

1.200 

1.5500 

0. 600 

7 

A 

At 

lAs 

6 A 

lAs 

13 

10 Vi 

1.300 

1.6750 

0. 600 

7A 

V, 

A 

lAs 

1A 

lAs 

14 

11 A 

1.400 

1.8000 

0. 600 

8 

A 

A 

lA 

IVs 

l'A 

15 

12 

1. 500 

1.9281 

0. 600 

8As 

At 

A 

IVs 

lAt 

l'A 

16 

12^ 

1.600 

2.0531 

0.600 

9 As 

A 

A 

l H 

1 As 

l'A 

17 

13^ 

1.700 

2.1812 

0. 600 

9 A 

A . 

A 

1 'As 

i 2 A 

l'A 

18 

14 

1. 800 

2.3062 

0. 600 

10A 

As 

y 8 

IVs 

l'At 

l'A 

19 

14^ 

1.900 

2.4312 

0. 600 

10A 

As 

Vs 

A As 

i 2 A 

l'A 

20 

15M 

2.000 

2.5562 

0. 600 

11 A 

As ' 

Vs 

2 

l'A 

IVs 


BROWN & SHARPE 


1 

4 Vi 

0. 200 

0.317 

0. 5000 

2 7 A 

1/40 

At 

Vi 

A 

Vs 

2 

5 'A 

0.250 

0.377 

0.5000 

3'A 

1/40 

'At 

As 

Vi 

Vs 

3 

5A 

0.3125 

0. 450 

0.5000 

3Vs 

1/40 

At 

Vs 

As 

As 

4 

5jf 

0.350 

0. 501 

0.5000 

3 "As 

1/40 

'At 

As 

Vs 

A 

5 

6Vs 

0.450 

0. 614 

0.5000 

4 

1/40 

V 

As 

As 


6 

6 7 A 

0.500 

0. 680 

0.5000 

4Vs 

1/40 

V, 

Vs 

'A 

As 

7 

7'A 

0. 600 

0. 800 

0.5000 

4Vs 

At 

As 

H 

Vs 

"As 

8 

8 Vs 

0. 750 

0.976 

0.5000 

5 A 

'A. 

V 

Vs 

"As 

Vi 

9 

8 Vs 

0.900 

1. 152 

0.5000 

6 'A 

'An 

V 

lAs 

Vs 

Vs 

10 

9 Vi 

1.0446 

1.337 

0.5161 

Ws 

Vu 

At 

1 As 

1 

1 

11 

10^ 

1.250 

1.565 

0.5000 

7Vs 

Vs, 

At 

1.45 

l'A 

l'A 

12 


1.500 

1. 841 

0.5000 

8A 

V, 

V, 

1.45 

l'A 

l'A 

13 

12 

1. 750 

2. Ill 

0.5000 

8 H 

V, 

V 

1.62 

l'A 

l'A 

14 

12'A 

2.000 

2.382 

0.5000 

9 M 

V, 

'A 

1.62 

l'A 

l'A 

15 

13^ 

2.250 

2.654 

0.5000 

9 Vi 

V 

'A 

1.95 

l'A 

IVs 

16 

13 A 

2. 500 

2.924 

0.5000 

iom 

'As 

% 

1.95 

l'A 

IVs 

17 

13 Vi 

2. 750 

3. 195 

0.5000 

10^ 

As 

*64 

1.95 

1 A 

IVs 

18 

14 H 

3.000 

3.466 

0.5000 

11^ 

As 

% 

1.95 

1 % 

IVs 


44 



















































FOR M O T O R MACHINISTS 


DRILLING* 


DRILLS.—A drill is an end-cutting tool, consisting usually 
of two cutting edges set at an angle with the axis. The 
more common types of drills are flat—flat-twisted—straight 
fluted—spiral-fluted—and gun-barrel. The most common, 
and for most purposes the most efficient type, is the spiral- 
fluted, known as a twist drill. 

Twist drills are made with two, three, or four cutting lips. 
The four-lip drills are used for en¬ 
larging holes previously cored or 
drilled. When drilling solid stock 
with a two-lipped drill, the point 
of the drill controls the cutting 
edges, and if the drill is correctly 
ground the resulting hole will be 
reasonably round, straight, and the 
size of the drill. When a drill is 
used for enlarging holes already 
made, either by coring or by pre¬ 
vious drilling, the drill is guided 
by its sides and a three or four 
fluted drill will give better results. 

There are three principal parts to 
a twist drill—the point, the body 
and the shank, as shown in Fig. 41. 

The point is the entire cone- 
shaped surface at the cutting end of 
the tool. The two or more spiral 
grooves running along the sides of 
the body of the drill are called flutes and serve four pur¬ 
poses. They help form the cutting edges of the point; they 
curl the chip so that it occupies the minimum space; they 
provide a means for the chip to escape from the drill hole; 
and they serve to convey the lubricant or cutting oil to the 

♦See pp. 47, 63, 97, 174 and 175, Vol. I, Starrett Books. Also pp. 10-12, 
Vol. II, Starrett Books. 



Drill Parts 


45 












THE 


STARRETT 


ROOK 


cutting edges of the tool. The shank provides a means of 
holding the drill in the drill press. 

Referring again to Fig. 41, it will be seen that portions of 
each of the three principal parts of the drill have names. 
The tip of point, or cone-shaped section, is called the dead 
center, and if the drill is to cut properly, this dead center 
must exactly coincide with the axis of the drill. The edges 



Fig. 42 —Web of Drill (Shown by Dark Section) 

of the point which do the actual cutting are called the lips 
and the portion of the point back of the lips is known as the 
heel. The narrow strip (A-B, Fig. 41) running along one 
edge of each flute is called the margin. It forms the outside 
cutting edge of the drill body and is the full diameter of the 



Fig. 43— Four Types of Drill Shank 
(1) Bit Stock (2) Straight 

(3) Taper (4) Ratchet 


drill. At point B (Fig. 41), the drill is relieved by what is 
called body clearance. The web, as shown in Fig. 42, ex¬ 
tends along the central axis of the drill and runs the entire 

46 
























FOR MO TOR MACHINISTS 


length of the body. It thickens toward the shank of the 
tool and gives the drill the necessary stiffness and strength. 

The four common types of shanks used on drills are shown 
in Fig. 43. They are, from left to right, the bit stock shank, 
the straight shank, the taper shank and the ratchet shank. 
Straight and taper shanks are the types most commonly 
used in automobile work. 

FORM OF POINT.—All 
drills used in ordinary ma¬ 
chine shop practice, except 
gun-barrel drills, are cone- 
pointed on the cutting end. 

The gun-barrel drill, used 
when especially straight, 
round, and true holes are 
essential, has a blunt end 
with a single cutting lip. 

A cone-pointed drill of 



Fig. 44—Twist Drill—Point 
Incorrectly Ground 


two or more cutting lips depends for its efficient working 
upon four factors: 

(a) All the cutting lips shall have the same inclination 
to the axis of the drill. 

( b ) Cutting lips should be of exactly equal length. 

(c) A proper lip clearance of the surface back of the 
cutting edges. 

(d) A correct angle of lip clearance. 


Figures 44, 45 and 46 show the result of careless free-hand 
grinding. Figs. 47 and 48 show one method of testing the 
length of the cutting lips, also their inclination to the axis. 
A better method, however, is to make use of a drill point 
gage (See Fig. 54), which checks at a single operation both 
the length of the lips and their angles with the axis of the 
drill. 

After sharpening a drill free-hand, use the hand-feed at 
first and observe (a) the chips made by the cutting; ( b ) the 
size of the hole. If the cutting lips are shaped to a proper 

47 








THE 


STARRETT 


ROOK 



clearance, the chips will curl as they start from the cutting 
edge. If the cutting lips lack a proper clearance, the result¬ 
ing chips have the appearance of being ground off rather 
than freely cut. If the cutting lips are of uneven length the 

hole will be enlarged over the 
diameter of the drill. Drill¬ 
ings from cast iron should 
look as in Fig. 57, and those 
from steel as in Fig. 58, if 
the drill is properly sharp¬ 
ened. 

Free-hand grinding results 
are usually so disappointing 
that in most machine shops 
the drills are sharpened in a 
special drill-grinding machine. The design of this machine 
is such that when it is set for grinding any size of drill the 
cutting lips are made of equal length and of the correct form. 
Fig. 59 shows how the cutting lip is located to grind the edges 
correctly. When grinding drills, care must be taken to avoid 
drawing the temper of the tool. 

It may be safely and con¬ 
servatively stated that 90 per 
cent of all drill troubles are 
the result of faulty grinding 
of either point or lip clear¬ 
ance. As was shown in Fig. 

41, the lips are the cutting 
edges of the drill and are 
formed by grinding the point 
at such an angle that the 
dead center coincides ex¬ 



Fig. 46 


actly with the axis of the drill — thus making the lips of 
precisely equal length—and then grinding away, or backing 
off or relieving the heel, as is shown at the right of Fig. 47. 
Note the difference between the drill point at the right of 
Fig. 47 and that shown at the left. The drill at the left has 
48 













FOR M 0 T 0 R MACHINISTS 


been ground so that the cone-shaped surface is at right angles 
to the axis of the drill and as a result has no cutting edge. 
In order that the drill may cut, or enter the metal, the sur- 



Fig. 47 —Correct (Right) and Incorrect (Left) Grinding 
Point Clearance 

faces S, see Figs. 48 and 49, must be ground away, so that 
the heel line B is below the cutting lip A, as is shown in 
Fig. 49. 



Fig. 48 —Drill Ground Fig. 49 —Drill Ground with 

without Lip Clearance Proper Lip Clearance 

Figure 50 show r s the angle—12° to 5°—at which heels 
should be relieved from the cutting edge. The angle is 
measured at the circumference or outer edge of the drill and 
should increase as the center of the drill is approached. 

When a properly ground drill is working in a hole, its 
condition will be similar to that shown in Fig. 51, where the 

49 













THE 


STARRETT 


BOOK 



Fig. 50—Proper Angle for Grinding Lip Clearance 

cutting lip has already removed considerable metal in advance 
of the heel, as is indicated by the dark sections on either side 
of the drill. 



Fig. 51—Correctly Ground 
Drill Working in Hole 



Fig. 52— Too Much Lip 
Clearance 


LESS 



Fig. 53—Too Little Lip Clearance 

50 










FOR MOTOR MACHINISTS 



Fig. 54—Drill Ground with Fig. 55—Drill Ground with 


Correct Lip Angles Too Flat a Point 


When too much lip clearance—over 12° to 15°—is given 
a drill point, as is shown in Fig. 52, the cutting edges are 
weakened so that they cannot withstand the pressure of 
drilling and will chip off or burn away. 

Insufficient lip clearance—less than 12° to 15°—makes it 
difficult for the drill to enter the metal and often causes 
splitting of the drill as shown in Fig. 53. 

A properly ground drill has its lips exactly the same in 
length and the angle the cutting 
edge makes with the axis of the 
drill is 59° as shown in Fig. 54. 

If the angle the cutting edge 
makes with the axis of the drill 
is more than 59°—even though 
the lips of the drill are equal in 
length—the tool will not center 
properly, because the cone- 
shaped point which is intended 
to hold it in its central position 
will be too nearly flat, See Tf 0 

Fig. 55. If the angle is less ^ ® o' 

than 59° see Fig. 56-the 

51 

























THE 


STARRETT 


BOOK 




drill will require more driving power because of the increased 
length of the cutting edges. 

If the cutting edges or lips have the same and correct 
angle, but are of different length, the point will necessarily 
be off center and the hole will be larger than the drill and 
irregularly shaped. Incidentally, a drill improperly ground 
not only destroys both itself—in addition to doing poor work 
—but is also destructive of the drill press because of the 
weaving of the spindle caused by the point of the drill not 
being held in alignment with the spindle of the drill press. 















FOR M OTOR MACHINISTS 


CUTTING COMPOUNDS*. To maintain high cutting 
speeds, it is necessary to use a lubricant. Those recom¬ 
mended have stood the test of service: 

For hard and refractory steel —Turpentine, kerosene, or 
soda water. 

For soft steel and wrought iron —Lard oil or soda water. 

For brass —Paraffine oil. 

For aluminum —Turpentine, kerosene, or soda water. 

For cast iron —A jet of air if anything is used—usually 
worked dry. 

LAYING OUT 

Locating the centers for drilled holes upon the body of 
the work is termed “laying out”. On the smaller jobs, 
laying out and drilling are usually done by the workman. 
Larger amounts of work warrant a skilled “layer out”. 

Laying out for drilling comes under two heads, viz.: 
Approximate and Accurate. Unless the holes when drilled 
are to match up with other holes or with fixed studs, it is 
usually sufficiently accurate if the center is laid off with a 
chalk pencil and a steel rule. For jig, tool, and experimental 
work, the centers must be accurately laid out and scribed 
upon the surface of the work. The practice is to scribe two 



Fig. 60 

•For cutting lubricants used in various operations see also p. 10, Vol. II, Starrett 

aok8 ' 53 













THE 


STARRETT 


ROOK 


or more lines which intersect at the exact desired point as 
shown in Fig. 60. Assume that the link is to connect two 
studs. Proceed to scribe two intersecting lines upon one of 
the hubs, as shown in Fig. 60, using a combination square 
fitted with a center head. At the intersection, accurately 
place a light center-punch indentation. Place one leg of a 




spring divider with its point in the center mark and adjust 
the other leg to have its point touch the edge line of the hub 
and note the concentricity of the center. If correct, close 
dividers to scribe a circle the diameter of the required drilled 
hole, setting the points by the scale graduations upon a 
steel rule. Locate light center-punch marks on the scribed 
circle as shown in Fig. 61. 

When the work is laid out by another than the driller, a 
second circle, having a slightly greater diameter, should be 
scribed. This check will show whether the hole was drilled 
54 



























FOR MO TOR MACHINISTS 


to the original layout. If no importance is attached to the 
center to center distance of the holes proceed as before with 
the second hub. Where the center to center distance is 
important, set the points of the universal dividers to the 
center length, and with the point A, Fig. 62, in the previously 
located center mark scribe on the opposite hub. Scribe a 
short line across its face afterward, proceeding as before. 

For accurate work, the use of the automatic center-punch 



Fig. 63—Scribing Circles with Dividers 

(Fig. 64) is recommended, as is the machinists’ center-punch 
(shown in Fig. 65), for heavy work. 

PREPARING THE SURFACE. For accurate laying 
out, clean the machined surfaces and wet the portion to be 
worked upon with a copper sulphate (blue vitriol) solution. 
To prepare a copper sulphate solution of the proper strength, 
dissolve one ounce of copper sulphate (commonly called blue 
vitriol) in four ounces of water to which has been added a 
scant teaspoonful of nitric acid. When dry, the surface as 
treated will distinctly show any lines which are made upon 
it. Chalk, well rubbed into the surface, is sufficient for the 
less accurate jobs. 

STARTING THE DRILL. After laying out and pre¬ 
vious to drilling, enlarge the center holes with a center-punch 

55 








THE 


STARRETT ROOK 



to assist the starting of the drill. Start the hole 
with drill pointin the enlarged center, using hand- 
feed until the nose of the drill is well started in 
the work. Observe if this is central with the 
scribed circle, and if not central use center 
gouge, as in Fig. 66, and repeat until accurate. 

TO DRAW A DRILL. When start¬ 
ing a drill it often has a tendency to 
slide or crowd off to one side. Where 
it is essential that the drilled hole coin¬ 
cide or center with some previously 
scribed circle or layout, the drill must 
be brought back into the correct position. 

This is accomplished by the use of a 
small gouge-pointed chisel, sometimes 
called a center chisel, and the process is 
termed “drawing the drill”. First, note 
toward which side of the small dimple 
left by the drill point it is necessary to 
shift the drill. Then chisel a small groove 
in that side of the dimple. 

If the start is very eccentric, several 
chisel grooves may be necessary; where¬ 
as, if only slightly eccentric, a mere touch 
of the chisel will often suffice. It is 
readily seen that the drill is made 
to cut more easily where the grooves 
are, and therefore the natural resistance 
of the opposite side pushes the drill 
toward the side cut by the gouge-pointed 
chisel. Drill drawing can only be done 
previous to reaching the full diameter 
of cut. 

HOLDING THE WORK. Careless¬ 
ness in holding the work is responsible 
for many drilling accidents. If no special 

56 


Fig. 64 


Fig. 65 

























FOR MOTOR MACHINISTS 


holding device is available, the work should be held in a 
drilling vise, clamped directly to the drilling-machine table, 
or clamped to an angle iron. Fig. 67 illustrates a method 
of holding the work safely. When once the work is clamped 
in position on the drilling-machine table, adjust the table to 
center the located hole with the drill rather than reclamp the 
work. When drilling on a speed-lathe the same caution 
should be taken. Do not hold work in the hand, use a vise 
or the steady rest. 

HOLDING THE DRILL. In Fig. 68, at A, the drill is 
shown held directly in the spindle. This is a good method 
if several holes of the same diameter are to be drilled at a 
single setting. When frequent changing of the drill is neces¬ 
sary, as in drilling holes of various different sizes, some form 
of quick-acting collet chuck should be used with single¬ 
spindle machines. The changes can then be made without 
stopping the machine. 

DRILL PRESS 

A common type of back-geared, upright drill press is shown 
on page 59, the various parts and their functions being 
indicated by the notations on the drawing. 

USING TWIST DRILLS 

In using twist drills too much attention can scarcely be 
given to speed and feed of the drill. Speed, ordinarily, does 
not refer to revolutions per minute, but to the peripheral or 
circumferential speed of the drill. In other words, the dis¬ 
tance the drill would travel if it were laid on its side and 
rolled. Thus, a drill speed of 30 feet per minute means that 
the tool—traveling on its side—would roll 30 feet in one 
minute. Feed is the distance per minute the drill advances 
in the work and feed pressure is the pressure required to 
maintain this rate of advance. 

The correct feeds and speeds to use in drilling vary widely 
with the character of the metal being drilled, the character 

57 



THE 


STARRETT 


BOOK 


SPEEDS AND FEEDS FOR DRILLING, USING CARBON 

STEEL DRILLS 

(High-Speed Steel Drills run 100% faster) 



Bronze 

Annealed 

Hard Cast 

Mild Steel 

Malleable 



Brass 

Cast Iron 

Iron c 

b 

Iron 

Cutting 

150' 

to 

00 

40' 

60' 

45' 

Speed 

per min. 

per min. 

per min. 

per min. 

per 

min. 

Size of 
Drill 

Feed 

Rev. 

Feed 

Rev. 

Feed 

Rev. 

Feed 

Rev. 

Feed 

Rev. 

Feed 

per 

Rev. 

per 

min. 

per 

min. 

per 

min. 

per 

min. 

per 

min. 

per 

min. 

per 

min. 

per 

min. 

per 

min. 

per 

min. 

Ins. 

Ins. 


Ins. 


Ins. 


Ins. 


Ins. 

2750 

Ins. 

V& 

.003 

9167 

27.5 

5195 

15.59 

2445 

7.33 

3667 

11.00 

8.25 

Y& 

.004 

4584 

18.3 

2597 

10. 39 

1222 

4.89 

1833 

7.33 

1375 

5.50 

% 

.005 

3056 

15.3 

1732 

8. 66 

815 

4.07 

1222 

6.11 

917 

4.51 

K 

.006 

2292 

13.8 

1299 

7. 79 

611 

3.67 

917 

5.50 

688 

4. 13 

% 

.007 

1833 

12.8 

1039 

7.27 

489 

3.42 

733 

5. 13 

550 

3.85 

Vs 

.008 

1528 

12.2 

866 

6.93 

407 

3.26 

611 

4.89 

458 

3.67 

% 

.009 

1310 

11.8 

742 

6.68 

349 

3. 14 

524 

4.72 

393 

3. 54 

H 

.010 

1146 

11.5 

649 

6.49 

306 

3.06 

458 

4.58 

344 

3.44 

% 

.011 

917 

10.1 

519 

5.71 

244 

2.69 

367 

4.03 

275 

3.03 

H 

.012 

764 

9.2 

433 

5.20 

204 

2.45 

306 

3. 67 

229 

2.75 

Vs 

.013 

655 

8.5 

371 

4.82 

175 

2.27 

262 

3.41 

196 

2.55 

i 

.014 

573 

8.0 

325 

4.55 

153 

2. 14 

229 

3.21 

172 

2.41 

in 

.016 

458 

7.3 

260 

4. 16 

122 

1.96 

183 

2.93 

138 

2.21 

iy 2 

.016 

382 

6.1 

216 

3.46 

102 

1.63 

153 

2.44 

115 

1.83 

m 

.016 

327 

5. 23 

186 

2.99 

87 

1.40 

131 

2.09 i 

98 

1.57 

2 

.016 

2S6 

4.58 

162 

2.60 

76 

1.22 

115 

1.83' 

86 

1.38 

2 X 

.016 

255 

4.07 

144 

2.30 

6S 

1.08 

102 

1.63 

76 

1.22 

2 *£ 

.016 

229 

3. 66 

130 

2.08 

61 

0.98 

92 

1.47 

69 

1.11 

2 H 

.016 

208 

3.33 

118 

1.89 

55 

0.88 

84 

1.34 

63 

1.00 

3 

.016 

191 

3.05 

108 

1. 73 

51 

0.81 

76 

1.22 

57 

0.92 


a. For cast steel, use half the speed shown for hard cast iron. 

b. For tool steel or drop forgings, use half the speed shown for mild steel. 

The figures above can be attained under ideal conditions, which cannot always 

be obtained in the shop. They form a mark at which to aim and thus show how 
far local shop conditions fall below the ideal. 


58 






































FOR MOTOR MACHINISTS 












































































































































































































THE 


STARR ETT 


BOOK 


of the steel from which the drill itself is made and the temper 
of the particular drill being used. 

Twist drills are divided into two classes according to the 
kind of steel from which they are made—carbon steel twist 
drills and high speed twist drills. The latter are more expen¬ 
sive, but can be operated at speeds greatly in excess of those 



Fig. 66 


permissible with carbon drills, and will do a correspondingly 
greater amount of work. High speed drills also hold their 
size better, require less sharpening and do more drilling in 
the same length of time than carbon drills. High speed 



drills should be used wherever possible, especially in all port¬ 
able electric drills, because the spindles of this type of drill 
usually run at speeds far too high for carbon drills of inch 
diameter and larger. 


60 


















FOR MOTOR MACHINISTS 


SELECTING SPEEDS AND FEEDS FOR 
DRILLS 

Common sense, experience and judgment are really the 
big factors in determining the correct drill feed and speed in 
each individual case. There are no hard and fast rules that 
can be invariably followed. Certain generalities and pre¬ 
cautions may, however, be observed to advantage. 



When starting a drilling operation in a power drilbpress, 
always bring the drill down to the work by hand feed until 
it is centered in the work. Then only can the power feed 
be safely thrown in. 


61 





























THE 


STARRETT 


BOOK 


When drilling soft tool or machinery steel with carbon 
steel drills it is safe to start with a speed of 30 feet per minute. 
In cast iron a speed of 35 feet and in brass 60 feet per minute 
may be safely used in starting the work. If high speed drills 
are used these speeds may be doubled. 

Recommended starting feeds vary according to the size of 
the drill and are the same for both high speed and carbon 
steel drills. For drills from to Y 2 in- a feed of from 
.004 to .007 in. per rotation is recommended, while for 
drills over Y 2 in. in diameter the feed should be .005 to 
.015 inch per revolution of the drill. Drills under /f6 inch 
take even lighter feeds than .004 inch. The secret of rapid 
drilling, as will be shown later, lies in using a light feed and 
the maximum permissible speed. This explains in part why 
more work can be done in the same time with high speed 
than with carbon drills. 

When starting a drill it is wise to use moderate feed and 
speed and increase either or both only after observing the 
condition of the drill, character of chips, etc. If a properly 
ground drill chips at the cutting edge or splits up the web, 
it is a pretty sure indication of excessive feed. Rapid wearing 
away at the outer corner of the cutting edge is evidence of too 
much speed. Attention should also be paid to the proper 
use of lubricant. (See page 53.) 

DRILLING FOR REAMER. When it is essential that 
the holes be of an exact diameter, it is customary to use-a 
drill somewhat smaller than the given diameter, and after¬ 
ward ream the holes to the desired size. The amount left 
for reaming depends upon whether one or two reaming opera¬ 
tions are necessary, and whether or not the reaming is to be 
done with a power reamer directly in the drilling machine. 
If the drilling is done through jig bushings and the holes 
are short as compared to their diameter, a single reaming 
operation will often suffice. If the holes are relatively long, 
the drill should be 1/64 in. to l/32 in. smaller than the 
finished hole diameter, to allow for passing a machine reamer 

62 



FOR MOTOR MACHINISTS 


.005 in. small through the hole which is afterward hand 
reamed. This method gives results as accurate as any, except 
by grinding, and is accepted practice for good work. 

DRILLING FOR TAPPING. Where a full thread depth 
is essential the hole to be tapped should be made with a drill 
of a diameter smaller than the nominal diameter of the bolt 
by an amount equal to double the depth of the thread. In 
practice the nearest commercial size of drill is listed for drill¬ 
ing tapped holes. The judgment of the operator, however, 
is the surest and safest guide in 
determining the proper size of drill 
to use. 

DRILLING LARGE HOLES. 

Twist drills range in size from No. 

80 wire gage to four inches in 
diameter. As the drill increases in 
diameter the web is correspond¬ 
ingly thickened, and as the cutting 
edges at the web do not cut as 
effectively as they do outside the 
web thickness, considerable pres¬ 
sure is required to force the larger 
drills into the work at an efficient 
speed. For this reason many workmen first drill a lead 
hole, using a drill whose diameter approximates the web 
thickness of the larger drill, as shown in Fig. 69. A lead 
hole will also assist in centering the drill upon an inclined 
surface. However, if the inclination is considerable it is 
necessary to butt mill or hand chip a spot giving sufficient 
surface to work upon. The practice of some firms engaged 
in production work, manufacturing, etc., is to use—in place 
of a single large drill—a relatively smaller one, afterward 
enlarging the hole by some method of counterboring at a 
much less expense for tools and at as rapid a production rate 
as by drilling the entire job. 

BOLT HOLES. When the bolts are for holding purposes 

63 













THE 


STARRETT 


ROOK 


only and are not used for aligning the several pieces, it is cus¬ 
tomary to drill the holes through which the bolts pass some¬ 
what larger than the bolt diameters. This allows for a variation 
in the bolt sizes and for inaccuracy in locating the centers. 

DEEP HOLE DRILLING. Under this name may be 
classed the drilling of holes through the axes of spindles, cam 
and crankshaft, push-rods, etc. While for spindle drilling it 
is possible to use ordinary twist drills with extended shanks, 
it is customary in efficient drilling of this sort to use special 



Fig. 70 

drills designed for the purpose. Fig. 70 shows a special hollow 
drill often used for drilling axial holes in spindles, and Fig. 71 
shows the machine with the drill guides in working position. 

In all cases of deep hole drilling it is better to rotate the 
work rather than the drill. The drill must be started exactly 
concentric with the axis of the machine. For this reason a 
starting-hole the exact diameter of the drill is first counter- 
bored. 

COUNTERBORING. There are many cases in which it 
is desirable to enlarge a hole throughout a portion of its 



Fig. 71 

64 




































FOR MOTOR MACHINISTS 


length. If a drill is used for this purpose there is no cer¬ 
tainty that the two diameters will be concentric. The prac¬ 
tice is to enlarge the already drilled hole by using a cutting 
tool having a pilot or leader to guide the cutting edges. 
This tool is known as a counterbore, and its use is termed 
counterboring. Fig. 72 shows the tool in operation and its 
purpose. 





NUMBERED TWIST DRILL SIZES 

The usual drill set consists of numbers from 1 to 60. The 
smaller sizes are not so much used in automobile shops. 
Sets of alternate sizes, 1, 3,5, etc., can also be bought. Drills 
down to about 40 have the numbers stamped on the shanks. 
The smaller ones have to be gaged. 

LETTER SIZE TWIST DRILLS 

The letter size twist drills are a continuation from the 
numbered sizes and are very useful for exact tap drill sizes 
in between the fractional sizes and to bridge the gap between 
the largest numbered size and the % in. drill which is often 
the smallest fractional size drill stocked. 

65 

























THE 


STARRETT 


ROOK 


Numbered Twist Drill Sizes 


No. 

Diam. 

No. 

Diam. 

No. 

Diam. 

No. 

Diam. 

No. 

Diam. 

No. 

Diam. 

1 

.228 

15 

. 180 

28 

. 141 

41 

.0960 

55 

.0520 

68 

.0310 

2 

.221 



29 

. 136 

42 

.0935 



69 

.0292 

3 

.213 

16 

. 177 

30 

. 129 

43 

.0980 

56 

.0465 

70 

.0280 

4 

.209 

17 

.173 



44 

.0860 

57 

.0430 



5 

.206 

18 

. 170 



45 

.0820 

58 

.0420 

71 

.0260 



19 

. 166 

31 

. 120 



59 

.0410 

72 

. 9250 

6 

.204 

20 

.161 

32 

.116 

46 

.0810 

60 

.0400 

73 

.0240 

7 

.201 



33 

.113 

47 

.0785 



74 

.0225 

8 

.199 

21 

.159 

34 

.111 

48 

.0760 

61 

.0390 

75 

.0210 

9 

. 196 

22 

. 157 

35 

. 110 

49 

.0730 

62 

.0380 



10 

.194 

23 

. 154 



50 

.0700 

63 

.0370 

76 

.0200 



24 

. 152 

36 

. 1065 



64 

.0360 

77 

.0180 

11 

.191 

25 

. 150 

37 

. 1040 

51 

.0670 

65 

.0350 

78 

.0160 

12 

. 189 



38 

.1015 

52 

.0635 



79 

.0145 

13 

.185 

26 

.147 

39 

.0995 

53 

.0595 

66 

.0330 

80 

.0135 

14 

. 182 

27 

. 144 

40 

.0980 

54 

.0550 

67 

.0320 




Letter Size Twist Drills 


Let¬ 

ter 

Frac. 

Deci. 

Let¬ 

ter 

Frac. 

Deci. 

Let¬ 

ter 

Frac. 

Deci. 

Let¬ 

ter 

Frac. 

Deci. 

A 

15 ^4 

.234 

H 

% 

.266 

O 

% 

.316 

U 

_ 

.368 

B 


.238 

I 


.272 



V 

H 

.377 

C 

— 

.242 

J 

— 

.277 

P 

n 4i 

.323 

w 


.386 

D 

_ 

.246 




Q 


.332 

X 


.397 

E 

H 

.250 

K 

% 

.281 

R 


.339 

Y 


.404 



L 


.290 

S 


.348 

z 


.413 

F 

— 

.257 

M 


.295 

T 


.358 




G 

— 

.261 

N 


.302 







DRILL SIZES FOR TAPS 

Every motor mechanic knows that a hole must be drilled 
before a thread tap can be used. Many, however, do not 
realize the close relationship between the size of the drill and 
that of the tap which follows it, nor do they know the reason 
for the relationship. It is perfectly obvious that the drill 
must be slightly smaller in diameter than is the tap which 
cuts the thread in the hole, for if the hole was drilled to the 
exact size of the bolt or stud it is to take, there would be no 
metal left in which to cut the threads. The proper drill for 
each size of thread tap is called the tap drill and the differ¬ 
ence in diameter between taps and tap drills is regulated by 
the character or kind of thread to be cut in each instance. 

66 












































FOR MOTOR MACHINISTS 


1 j. 1 1 BOLT 


Obsolete v- thread < 

C7 THDS. PER IN.) 


-60°THD. 


i. 


B 


NATIONAL COARSE THREAD 
(U.S. STD.) 

(7 THDS. PER IN.) 


The explanation for this difference in the size of the tap 
drill used for the same sized tap in these threads is found 

in the effect of the type of 
thread to be cut and the dif¬ 
ference in the number of 
threads to the inch. Fig. 
73A shows the drill hole 
required for a 1J4 inch “V” 
thread bolt. Note that the 
outside diameter of the 
threads is 1J4 hi., but that 
the drill hole required is but 
1 3/64 inch. Compare this 
with the U. S. S. bolt as in 
Fig. 73B. Since the U. S. S. 
thread has a flattened top 
and root, to reduce the 
amount of metal to be re¬ 
moved by the tap, a larger 
drill is used. The space be¬ 
tween the two inner sets of 
dotted lines indicates the 
difference in the amount of 
metal removed. Fig. 73C 
indicates in the same way 
the still larger drill required 
where the hole is to be 
threaded to take an S. A. E. 
bolt or machine screw. In 
this case, not only is the 
thread different from the V 
type, but the number of 
threads to the inch is 12, as 
compared with 7 for the V 
and U. S. S. types, making it even more necessary to re¬ 
move a greater amount of metal before attempting to tap 

67 


National Fine Thread 
(S.A.E.) 

(12 THDS. PER. IN.) 


60*THD. 

FLAT 

BOTTOM 

TOP 


60°THD. 
FLAT 
; BOTTOM 
M TOP 


-i i 

i 7 "HOLE 
1 64 

, 11" HOLE 
-1 64 


Fig. 73 —Comparison of Tap 
Drill Sizes Required for 
Bolt Holes of Same Diam¬ 
eter “V”, U. S. S., and S. A. E. 
Threads 






















THE 


STARRETT 


ROOK 


the hole. The different sizes of tap drills required for taps 
for “V”, U. S. S., and S. A. E. Threads are given in the tables 
in this section. 

When drilling holes to be threaded, some consideration 
should be given to the material on which the work is done 
and to the depth of the tapped hole. Generally speaking, 
soft, tough material, such as copper, Norway iron, drawn 
aluminum, etc., should have a larger hole drilled for the tap 
than is necessary when working in mild steel, cast iron, etc. 
Also, on soft, tough material, the sharpness of the tap is more 
important than with brass, steel, cast iron, etc. 


COMPARISON OF TAP DRILL SIZES FOR DIFFERENT THREADS 


Bolt Diameter 

National Coarse Thread 
(Formerly U. S. Std.) 

National Fine Thread 
(Formerly S. A. E.) 

No. 1 

No. 53 

No. 53 

2 

51 

50 

3 

47 

46 

4 

44 

42 

5 

39 

38 

0 

36 

33 

8 

29 

29 

10 

26 

21 

12 

17 

15 

X 

8 

3 

% 

x 

% 

X 

% 


7 A 

1% 

2S A 

X 

27 A 

2 % 

% 

Sl ^4 

SS A 

fi 

17 * 

i7 A 

X 

2 'A 

l % 

y* 



i 

% 


i x 

#3 4 

1% 

1 X 


v% 

ix 

1 2 !4 


i X 

i 35 ^ 

1 4 % 

2 

l* 5 ^ 

1 5 % 

2X 


2% 

2X 

2 H 

2 13 A 

2 H 

2'A 

2 21 A 

3 

2% 

2 S7 A 


68 













Continuous Drill Table 


Sizes starting with No. 80 and going up to 1 inch. This 
table is useful for quickly determining the nearest drill size 
for any decimal, for root diameters, body drills, etc. 


Drill 

No. 

Frac. 

Deci. 

Drill 

No. 

Frac. 

Deci. 

Drill 

No. 

Frac. 

Deci. 

Drill 

No. 

Frac. 

Deci. 

80 

_ 

.0135 

42 


.0935 

7 


.201 

X 


.397 

79 

— 

.0145 

— 

Hi 

.0938 


'Hi 

.203 

Y 

— 

.404 

— 

Hi 

.0156 



6 


.204 




78 

77 

— 

.0160 

.0180 

41 

40 

— 

.0960 

.0980 

5 

4 

— 

.206 

.209 

Z 

'Hi 

.406 

.413 

76 

75 

74 

= 

.0200 

.0210 

.0225 

39 

38 

37 

= 

.0995 
. 1015 
.1040 

3 

2 

Hi 

.213 

.219 

.221 

1 I 1 

2 Hi 

He 

2 % 

.422 

.438 

.453 

73 

— 

.0240 

36 


.1065 

1 

_ 

. 228 


'% 


72 

_ 

.0250 

— 

A 

_ 

.234 

— 

.469 



— 

Hi 

. 1094 



—- 

8 Hi 

.484 

71 

_ 

.0260 

35 


. 1100 

_ 

'Hi 

.234 

— 

y 2 

88 4 

. 500 

70 

_ 

.0280 

34 

— 

. 1110 

B 

.238 

— 

.516 

69 

— 

.0292 

33 

— 

. 1130 

C 

_ 

.242 

— 

l7 ^ 

.531 

68 

— 

.0310 




D 

— 

.246 




— 

Ht 

.0313 

32 

— 

. 116 

— 


.250 

— 

s % 

.547 




31 

— 

. 120 



— 

% 

.562 

67 

— 

.0320 

— 

'A 

. 125 

E 

— 

.250 

-. 

*16 

.578 

66 

— 

.0330 

30 


. 129 

F 

— 

.257 

-- 

'% 

.594 

65 

— 

.0350 

29 

— 

. 136 

G 

— 

.261 

— 


.609 

64 

— 

.0360 




— 


.266 



63 

— 

.0370 

— 

% 

. 140 

H 


.266 

— 

% 

.625 




28 


. 141 




-- 

4 Hi 

. 641 

62 

— 

.0380 

27 

— 

. 144 

I 

— 

.272 

-- 

2 Hi 

.656 

61 

— 

.0390 

26 

— 

. 147 

J 

— 

.277 

— 

4 % 

.672 

60 

— 

.0400 

25 

— 

. 150 

— 

% 

.281 

— 

'He 

.688 

59 

— 

.0410 




K 


.281 



58 

— 

.0420 

24 

— 

. 152 

L 

— 

.290 

— 

4 H 

.703 




23 

— 

. 154 




— 

2 Hi 

4 H 

.719 

57 

— 

.0430 

— 

% 

. 156 

M 

— 

.295 

— 

.734 

56 

— 

.0465 

22 


. 157 

— 


.297 

-. 

H 

.750 

— 

Hi 

.0469 

21 

— 

. 159 

N 


.302 

— 

4 % 

.766 

55 


.0520 




— 

He 

.313 



54 

— 

.0550 

20 

— 

. 161 

O 

.316 

— 

2 Hi 

.781 




19 

— 

. 166 




-- 

5 Hi 

.797 

53 

— 

.0595 

18 

— 

. 170 

P 

— 

.323 

— 

'He 

.813 

— 

He 

.0625 

— 

"A 

. 172 

— 

2 '4i 

.328 

— 

58 4’ 

.828 

52 


.0635 

17 


.173 

Q 


.332 

— 

2 % 

.844 

51 

— 

.0670 




R 

— 

.339 



50 

— 

.0700 

16 

— 

. 177 

— 

"A. 

.344 

— 

5 Hi 

.859 




15 

— 

. 180 



— 

7 A 

.875 

49 

— 

.0730 

14 

— 

. 182 

S 

— 

.348 

— 

5 Hi 

.891 

48 

— 

.0760 

13 

— 

. 185 

T 

— 

.358 

— 

2 Hi 

.906 

— 

% 

.0781 

— 

He 

.188 

— 

23 4 

.359 

— 

B Hi 

.922 

47 


.0785 



U 


.368 




46 

— 

.0810 

12 

— 

.189 

— 

Vs 

.375 

— 

'He 

.938 




11 

— 

. 191 



— 

6 Hi 

.953 

45 

— 

.0820 

10 

— 

.194 

V 

— 

.377 

— 

3 Hi 

.969 

44 

— 

.0860 

9 

— 

.196 

w 

— 

.386 

— 

6 % 

.984 

43 

— 

.0890 

8 


.199 

— 


.391 


1 

1.000 


69 






















THE 


STARRETT 


ROOK 


U. S. Standard Tap Drill Table 

The tap drills listed here will give about a 75-80% thread 
which is sufficiently strong to break the bolt before stripping 
the threads. A full thread can be tapped by drilling to the 
root diameter, but the breakage of taps will be heavy and no 
good will be gained. For rough work a 50% thread is con¬ 
sidered sufficient. 


Diameter 

Threads 

Per Inch 

Root 

Diameter 

Tap 

Drill 

K 

20 

.185 

No. 8 

He 

18 

.240 

K 


16 

.294 

He 

He 

14 

.345 


K 

13 

.400 

% 

96 

12 

.454 

% 

H 

11 

.507 

% 

K 

10 

.620 

% 

% 

9 

.731 


l 

8 

.838 

K 

1 Vs 

7 

.939 


IK 

7 

1.064 

1% 

IK 

6 

1.283 

1 % 

IK 

5 

1.490 

1% 

2 

4^ 

1.711 

1 2 $4 

2K 


1.961 

214 

2 ^ 

4 

2.175 

2K 

2 : K 

4 

2.425 

2y 2 

3 

4 

2.675 

2M 


Note: For threads above 3 in., areas of bolts, areas at roots, head and nut 
dimensions, etc., see The Starrett Book, Volume I, Page 78. 


70 










FOR MOTOR MACHINISTS 


SIZES OF TAP DRILLS FOR TAPS WITH 
U. S. S., S. A. E., “V”, AND WHITWORTH THREADS 


“V” Thread 

u. s. s. 

S. A. E. 

Whitworth 

Diam. 
of Tap 
in inches 

Threads 
per inch 

Size of 
Drill No 

Diam. 
of Tap 
in inches 

Threads 
per inch 

Size of 

Drill No. 

Diam. 

of Tap 

in inches 

Threads 

per inch 

Size of 

Drill No. 

Diam. 

of Tap 

in inches 

Threads 

per inch 

Size of 

Drill No. 

Vi 

20 

13 

Vx 

20 

8 

Vi 

28 

3 

Vi 

16 

Vo 

% 

18 

D 

% 

18 

Vi 

Vo 

24 

9 32 

Vo 

16 

15 4 

Vs 

16 

M 

Vs 

16 

Vo 

Vs 

24 

'K> 

Vs 

14 

% 

Vie 

14 


Vo 

14 


Vi 

20 

25 V 

Vi 

14 


% 

13 

Y 

V2 

13 

27 4 

V2 

20 

2 Vi 

V2 

12 

Vs 

% 

12 

29 4 

Vo 

12 

S1 4 

9 16 

18 

3 Ki 

— 

— 

— 

Vs 

11 

V2 

Vs 

11 

n ^2 

Vs 

18 

37 4 

Vs 

10 

y 2 

K 

10 


H 

10 

2 K 2 

K 

16 

l Vo 

K 

10 

% 

Vs 

9 

2 K 2 

Vs 

9 

49 4 

Vs 

14 

Vf 6 

Vs 

9 

23 /32 

l 

8 


1 

8 

Vs 

1 

14 

l V> 

1 

8 

2 K> 

l Ys 

7 

1 V 16 

IVs 

7 


IK 

12 

1 3, 64 

— 

— 

— 

1 Vi 

7 

1V6 

1V4 

7 

1% 

1 V 4 

12 

1"4 

— 

— 

— 

1 V2 

6 

l 9 /32 

1V2 

6 

l 21 4 

1 % 

12 

1 2 % 

— 

— 

— 

m 

5 

1 V4 

IK 

5 

l 35 4 

1M 

12 

1 43 4 

— 

— 

— 

2 

41/2 

l 23 ^2 

2 

41/2 

l 2 V/2 

2 

12 

1 59 4 

— 

— 

— 

2 Vi 

4% 

l 3 V£ 

2 V4 

4% 

2V6 

2 Vi 

12 

2^2 

— 

— 

— 

2 V2 

4 

2>ki 

2 V 2 

4 

2 Vi 

2 % 

12 

2 13 /32 

— 

— 

— 

2 M 

4 

2 2 % 

2 K 

4 

2 V2 

2M 

12 

2 21 ^2 

— 

— 

— 

3 

4 


3 

4 

2K 

3 

10 

2 57 4 

— 

— 

— 


NOTE: The drills recommended for various sizes and kinds of taps will leave 
enough metal to form approximately a 75-80 per cent thread. For exact sizes 
and percentages of threads obtained, see pages 97 and 98. 


71 





































THE 


STARRETT 


BOOK 


SCREW THREAD FITS 

The particular use to which a screw or nut is put may make 
quite a difference in the fit of the screw threads. The extreme 
case of a sloppy fit is a stove bolt and nut, usually used to 
hold sheet metal parts, fenders, aprons and other parts 
together. Here the nut is a loose and wobbly fit, but it 
is sufficient for the purpose. The other extreme is in main 
bearing studs and nuts .where the material must be of 
decidedly better grade than cold rolled steel and where 
the threads must be a very close fit so that the strain will 
be equally distributed between the different threads on the 
screw and nut. 

The American standard of screw threads, in addition to 
recommending certain basic sizes and thread pitches as 
shown in the tables on pages 97 and 98, has made definite 
recommendations for various classes of fits as follows: 

LOOSE FIT: Recommended as a commercial standard 
for tapped holes in the numbered sizes only. May be used 
with screws in other classes to obtain quality of fit desired. 

FREE FIT: Includes the great bulk of screw thread work 
of ordinary quality of finished and semi-finished bolts, nuts, 
etc. 

MEDIUM FIT: Includes the better grade of interchange¬ 
able screw thread work such as automobile bolts and nuts. 

CLOSE FIT: Includes screw thread work requiring a 
fine snug fit, somewhat closer than the medium fit, such as 
high grade aircraft parts, etc. In this class of fit selective 
assembly of parts may be required. It is not considered 
practicable as a commercial standard for tapped holes of the 
numbered sizes. 

It should be noted that the fit of a screw thread is con¬ 
trolled in the cutting of the thread and has no relation 
whatever to the diameter of the tap drill hole. Increasing 
the size of this hole simply takes off the crest of the nut 
thread, but in no way affects the closeness of fit of the rest 
of the thread. 


72 



FOR MOTOR MACHINISTS 


TAP DRILLS 

S. A. E. Screw Thread Table 

Adopted by the Society of Automotive Engineers, June, 
1911. Previously known as the A. L. A. M. thread. In¬ 
tended for use in steel and hard materials. Cast iron, bronze 
and aluminum should be threaded U. S. Std. The tap drills 
listed allow about 75% thread which is sufficiently strong to 
break the bolt before stripping the thread. 


Diameter 

Threads 
per Inch 

Tap Drill 

Diameter 

Threads 
per Inch 

Tap Drill 

K 

28 

No. 3 

H 

16 

n A 

% 

24 

% 

Vs 

14 

13 A 

H 

24 

"A 

1 

14 

U A 

% 

20 

25 4 

lYs 

12 

VVi 

If 

20 

29 6 

Vi 

12 

1% 

% 

18 


VA 

12 

VVi 

Vs 

18 

S7 4 





Above 13^2 i n - the S. A. E. threads have two pitches, coarse 
and fine. 


Diameter 

Coarse 

Fine 

Diameter 

Coarse 

Fine 

IVs 

12 

16 

3Vs 

10 

16 

1M 

12 

16 

4 

10 

16 

IVs 

12 

16 

4j4s 

10 

16 

2 

12 

16 

4 H 

10 

16 

2H 

12 

16 

4 % 

10 

16 

2 Vi 

12 

16 

VA 

10 

16 

2Va 

12 

16 

Vi 

10 

16 

2 y 2 

12 

16 

4 % 

10 

16 

2Vs 

2H 

12 

16 

4 Vs 

10 

16 

12 

16 

5 

10 

16 

2Vs 

12 

16 

5 X 

10 

16 

3 

10 

16 

5H 

10 

16 

3H 

3^ 

10 

16 

5V 8 

10 

16 

10 

16 

5V 2 

10 

16 

m 

10 

16 

5Vs 

10 

16 

3 H 

10 

16 

5 % 

10 

16 

ZVs 

10 

16 

5Vs 

10 

16 

3M 

10 

16 

6 

8 

16 


Sizes from 6 in. up have a coarse pitch of 8 and a fine pitch 
of 16. Sizes run by eighths. 

73 


























TAP AND BODY DRILLS 

Machine Screw Threads* 

The body drills listed are exact sizes of the screw. Where 
more clearance is desired use one or two sizes larger. The 
tap drills give a 75% thread which is sufficient. For steel, 
use one or two sizes larger. Threads marked (*) are National 
Fine Thread Series (S. A. E. Standard); those marked (t) 
are National Coarse Series (U. S. Standard) (See page 85). 


Tap 

Diam. 

Body 

Drill 

Tap 

Drill 

Tap 

Diam. 

Body 

Drill 

Tap 

Drill 

0-80* 

.060 

52 

56 

11-30 

.203 

6 

17 

l-64f 

.073 

49 

53 

12-20 

.216 

2 

19 

1-72* 

.073 

49 

53 

12-22 

.216 

2 

17 





12-24t 

.216 

2 

17 

2-48 

.086 

44 

51 

12-28* 

.216 

2 

15 

2-56t 

.086 

44 

51 





2-64* 

.086 

44 

50 

13-20 

.229 

A 

15 





13-22 

.229 

A 

15 

3-40 

.099 

39 

47 

13-24 

.229 

A 

13 

3-48f 

.099 

39 

47 





3-56* 

.099 

39 

46 

14-20 

.242 

D 

13 





14-22 

.242 

D 

11 

4-32 

.112 

33 

45 

14-24 

.242 

D 

9 

4-36 

. 112 

33 

44 





4-4 Of 

. 112 

33 

44 

15-18 

.255 

F 

10 

4-48* 

.112 

33 

42 

15-20 

.255 

F 

8 





15-22 

.255 

F 

6 

5-30 

.125 

30 

40 

15-24 

.255 

F 

5 

5-32 

.125 

30 

40 





5-36 

.125 

30 

39 

16-16 

.268 

I 

7 

5-40t 

.125 

30 

! 39 

16-18 

.268 

I 

6 

5-44* 

.125 

30 

38 

16-20 

.268 

I 

5 





16-22 

.268 

I 

3 

6-30 

.138 

28 

36 





6-32f 

.138 

28 

36 

17-16 

.282 

L 

6 

6-86 

.138 

28 

33 

17-18 

.282 

L 

2 

6-40* 

.138 

28 

33 

17-20 

.282 

L 

2 

7-28 

.150 

24 

32 

18-16 

.295 

N 

2 

7-30 

. 150 

24 

31 

18-18 

.295 

N 

1 

7-32 

.150 

24 

30 

18-20 

.295 

N 

B 

7-36 

. 150 

24 

29 









20-18 

.321 

P 

• F 

8-24 

. 164 

19 

30 

20-20 

.321 

P 

G 

8-30 

. 164 

19 

30 





8-32f 

. 164 

19 

29 

22-16 

.347 

S 

I 

8-36* 

. 164 

19 

29 

22-18 

.347 

S 

K 

9-24 

.176 

16 

29 

24-16 

.374 

V 

M 

9-28 

. 176 

16 

28 

24-18 

.374 

V 

N 

9-30 

.176 

16 

27 





9-32 

. 176 

16 

25 

26-14 

.400 

Y 

O 





26-16 

.400 

Y 

P 

10-24f 

.190 

11 

26 





10-30 

.190 

11 

22 

28-14 

.426 

We 

R 

10-32* 

.190 

11 

21 

28-16 

.426 

7 <4 

S 

11-24 

.203 

6 

21 

30-14 

.453 


u 

11-28 

.203 

6 

17 

30-16 

.453 

S9 ^4 

V 


*A table of Metric Screw Threads will be found in the Starrett Book, Vol. II 
page 136. 















FOR MOTOR MACHINISTS 


TAP DRILLS 

Pipe Threads and Specifications 

Brass, iron and steel pipe are made to the nominal sizes 
shown in the left column. The threads used in this country 
are known as Briggs standard, V-form, 60 dsg. with a taper 
of 24 in* P er foot. The actual diameter of the pipe is in all 
cases larger than the nominal diameter. 





-r- 

--— 




-c— 

i t~ 

Size 

Threads 
per Inch 

Tap 

Drill 

Outside 

Diamete 

Inside 

Diamete 

Size 

Threads 

per Inch 

Tap 

Drill 

If 

1.2 

OQ 

Inside 

Diamete 

% 

27 

21 4 

17 4* 

% 

17 ^ 

3 

8 

334 

334 

334 

18 

*36 

23 4 

334 

8 

3 14 4 

4 

3*34 

% 

18 


! !4 

A 







14 

»V6 

27 4s 

% 

4 

8 

434 

434 

436 

H 

14 

2 % 

134 

5 34 ' 

434 

8 

4 1 34 

5 

434 

l 

1134 

134 

i 2 36 

m 

i 25 4 

5 

8 

5M 

634 

534 

6|4 

534 


H34 

l 15 4a 

1 4 34 

6 

8 

614 

1134 

1 2 34 

1 2 36 

m 

7 

8 

— 

7 34 

7*4 

2 

1134 

234 

234 

2Vs 

2 % 

8 

8 

— 

834 

7 y 

234 

8 

234 

2*34 

9 

8 

—• 

934 

8 61 4 



10 

8 


10M 

1036 


STOVE BOLT THREADS 

The threads are U. S. Std. form, rolled and a loose fit. 


Diameter 

Threads 
per Inch 

Wrench * 
Opening 

For Nut 

Diameter 

Threads 
per Inch 

Wrench 

Opening 

For Nut 

XL 

32 

28 

£ 

H 

34 

18 

18 

I 

kL 

24 

H 

H 

16 

% 

22 

34 





75 































THE 


STARRETT 


ROOK 


WOOD SCREW SPECIFICATIONS 

Wood screws and machine screws are made to the same 
gage and corresponding numbers will be the same size. The 
body drill listed is the nearest size over the outside diameter 
of the shank of the screw. For more clearance use one or 
two sizes larger. The small drill size is recommended prac¬ 
tice. Unusual length screws or unusual woods may require 
a deviation from the sizes listed. Countersinks for flat head 
screws should be 82 degrees. 


Number 

Diameter 

Threads 
per Inch 

Body 

Drill 

Small D 

Hard 

Wood 

rill 

Soft 

Wood 

0 . 

.058 

32 

52 

56 

63 

1 

.071 

28 

49 

55 

56 

2. 

.084 

26 

44 

52 

55 

3. 

.097 

24 

40 

49 

52 

4. 

. 110 

22 

35 

45 

51 

5. 

.124 

20 

30 

42 

48 

6. 

.137 

18 

28 

38 

45 

7. 

.150 

16 

24 

33 

42 

8. 

.163 

15 

19 

31 

40 

9. 

.176 

14 

16 

30 

33 

10. 

.189 

13 

12 

28 

32 

11. 

.203 

12 

6 

25 

31 

12. 

.216 

11 

2 

20 

30 

13.. 

.229 

11 


16 

28 

14. 

.242 

10 

H 

14 

26 

15. 

.255 

10 

ll 4i 

12 

23 

16. 

.268 

9 

% 

8 

19 

17. 

.282 

9 


4 

17 

18. 

.295 

8 

19 ^ 

3 

16 

19. 

.308 

8 

% 

1 

12 

20. 

.321 

8 

2, 4 


8 

21. 

.334 

8 


H 

6 

22.. . . 

.347 

7 


17 4 

2 

23. 

.361 

7 

f? 



24. 

.374 

7 

% 

,7 4 


25 . 

.387 

7 

25 4 

% 


26 . 

.400 

6 

n /n 

'% 

M 

27. 

.413 

6 

27 « 

'% 

H 

28. 

.426 

6 

tie 

% 

,7 4 

29. 

.439 

6 

2 Y4 


,7 4 

30 . 

.453 

6 

29 4 

l \4 

% . 


Courtesy of Motor World. 

76 












































FOR MOTOR MACHINISTS 


TAPS 



Fig. 74 —Starting, Plug and Bottoming Taps 

The commonest form of hand tap is the plug tap, shown 
in Fig. 74B. This tap has a bevel or chamfer at its outer 
end, the bevel extending back about 5 to 6 threads. This 
taper enables the tap to enter the hole easily, each succeed¬ 
ing tooth deepening the cut of thread until the tool has 
entered to a point above the taper, where it cuts the full 
size of the tap. When, however, it is desired to tap to the 
bottom of a blind hole, that is, one which does not go all the 
way through—as for cap or stud bolts—a bottoming tap, 
shown in Fig. 74C, is used. Usually a blind hole is first 
tapped as deep as possible with a plug tap and the job 
finished with a bottoming tap. On large holes use is often 
made of a starting tap, Fig. 74A, which cuts part of the 
thread; the plug tap is used next and, if necessary, a bottom¬ 
ing tap is employed to finish the job. 

77 






































THE 


STARRETT 


ROOK 


USING TAPS 

Hand taps can be used either in a tap wrench, in tapping 
attachments, or a chuck for machine tool work. When using 
it as a hand tool it should be placed in a tap wrench, rather 
than in a monkey wrench, as the latter exerts pressure only 
on one side with the result that a clean, true thread is diffi¬ 
cult to obtain. In addition to the difficulty encountered in 
obtaining a true thread when a monkey wrench is used on a 
tap, even more serious trouble often results from the break¬ 
ing of the tap. When starting a tap, a small try-square can 
often be used to advantage to make sure that the tap is 
starting square with the surface of the work. The square 
should also be used occasionally during the work to check 
squareness. 

When tapping, it is customary to turn the tap to the right 
(or left, as the case may be), cut a little way and then back 
off or reverse a turn or so in order to give the chips a chance 
to fall away from the tap and work out through the flutes of 
the trap. Lubricant—as was recommended for drilling— 
should be used freely. 

REGRINDING TAPS 

When taps are reground, care should be taken to see that 
the same amount of metal is ground from each flute. For 
grinding the cutting edge of a tap, the edge or corner of the 
grinding wheel should be dressed off to the approximate 
radius of the flute so that the hook, or under-cut, is pre¬ 
served. Grind one edge of the tap at a time, removing the 
same amount from each flute. The tap should be passed 
under and the cutting edge brought against the wheel with 
an easy, light pressure. Be very careful not to grind the 
heel or rear of the next land. Care should also be taken 
not to draw the temper of the tool. The chamfer of approx¬ 
imately five threads on the nose of a plug tap should be 
carefully preserved. Figure 75 shows an end view of a tap 
and gives the names of the various parts. 

78 



FOR M O T 0 R MACHINISTS 


Note that the lands, shown in Fig. 75, are all relieved or 
backed off. This is to make the tap cut easier by reducing 
friction in the hole and at the same time providing an actual 
cutting edge to form the thread. Land X in Fig. 75 shows 
what is called “ordinal y relief”, and the dotted line on 
land Y, what is known as straight angle relief. Some taps 
are made with no relief at all on the lands. Taps of this 



Fig. 75—Section through Tap 


type will maintain their size longer and will permit regrind¬ 
ing as long as the land is heavy enough to stand the cut. 
They are, however, harder to use as the cutting edges tend 
to bind in the hole. Taps intended to be used in brass and 
similar soft metals have a rake to the cutting edge instead of 
a hook. That is, instead of being under-cut, the angle of 
the cutting edge is in an opposite direction as shown by land 
Z in Fig. 75. For tapping holes in copper and similar stringy 
metals, taps with staggered teeth are obtainable. A tap of 
this sort may be made by cutting out alternate teeth on 
each flute, thus providing additional space and freedom for 
chip clearance. 


To Remove a Broken Tap 


Motor machinists and repair men are particularly liable 
to meet with trouble from taps breaking. While there are 
devices made specially for removing the broken portion of a 
tap from a hole, they are not always available or satisfactory. 


79 






THE STARRETT BOOK 


In such cases the broken tap may be removed by working 
as indicated in Fig. 76. 

Two men are needed to remove a broken tap in this man¬ 
ner. Using blunt chisels, or drifts, which will not break the 
lands, they drive simultaneously and on opposite lands. 
Clear the hole of chips and use light blows at the start. 
Nitric acid may also be used for loosening a tap, diluting it 
to the proportion of one part of acid to two parts of water 
and pouring it into the hole. When this method is followed, 
the hole should be thoroughly washed out with water, or 
better with household ammonia, to prevent the acid con¬ 
tinuing to eat into the threads. 



Fig. 76 —Proper Method of Removing Broken Tap by Working 
Simultaneously on Both Sides 

USE AND CARE OF DIES 

The function or work of a threading die or screw plate is 
exactly the reverse of that performed by a tap. Whereas a 
tap cuts an internal thread, as for example on a nut, the 
corresponding die is used to cut the proper thread on a bolt 
to fit that nut. 

The following are the common forms of dies: Die stock 
die, solid die, spring threading die, adjustable round-split 
die, rethreading die, and self-opening dies of various designs. 
The die stock die is made with inserted chasers—or cutters 
—which can be adjusted to size and can be resharpened 
by grinding on the cutting edge. Four chasers are generally 
used in this type of die, though some styles have two chasers 
80 















FOR MOTOR MACHINISTS 


with four cutting edges. The chasers are held in place 
by screws on the face, set in on an angle and bearing in a 
slot at the sides. Two sets of screws in the rear of the 
plate provide means of adjusting the die to size, the screws 
moving the ring which holds the chasers in place and bears 
on the taper at the back of each chaser, causing them to 
move in or out as the work may require. 



Die Stock Die and Extra Chasers 

For sharpening, the chasers are removed from the die and 
are ground on the cutting edge, care being taken to remove 
the same amount of metal from each chaser. If, as is seldom 
the case, the relieved face—or side opposite the cutting edge 
—has to be touched up, great care must be taken to see 
regular angle of relief is maintained as in tap-grinding. 

The solid die has no provision for adjustment and can be 
ground only on the chamfer or bevel at the front of the 
die. They are used exclusively for renewing worn threads 
and may be held in special holder or—as they are very 
often made hexagonal—in a common wrench. 




















THE 


STARRETT 


ROOK 


In the adjustable round-split die, compensation for wear 
is obtained by means of screws in the die stock which close 
in the die. These dies are sharpened in a manner similar 
to that used with solid and rethreading dies. 

A spring threading die is adjusted by springing in the 
cutting edges by means of a threaded or plain collar which 
moves back on a taper. Resharpening is done by grinding 



Adjustable Round-Split Die 


in the chamfer and also by grinding the cutting edges with 
a small, thin wheel which will go down into the slots. Spring 
threading dies may be held either in a chuck or tap wrench 
or in a special holder. 



Spring Threading Dies 


Chasers for dies are either milled or tapped. Milled 
chasers—those having teeth formed by a hob—are ground 
on the throat or chamfer and the cutting edge—where the 
type of die permits—is occasionally ground to keep it clean 
and sharp. Tapped chasers are ground on the cutting edges 
instead of on the throat or chamfer. 


82 







FOR MOTOR MACHINISTS 


In sharpening dies the following points are worth remem¬ 
bering: Grind all cutting points uniformly; keep the angle 
for relief, chamfer, etc., as near the original as possible. 

For cast iron, machine and ordinary cold rolled steel and 
for malleable iron, ordinary straight grinding of the chasers 



TAPPED DIE MILLED DIE 



TAPPED DIE MILLED DIE 


Ordinary Straight Chasers Ground 

Ground Chasers with Radial Hook 


is satisfactory. For tough materials, such as copper, alumi¬ 
num, nickel, steel, etc., grind the chasers with a slight radial 
hook. Just how much hook to use can be determined only 
by experiment or experience. 

For threading cast or bar brass, rubber or fiber, the chasers 
should be ground toward the center on an upward angle. 
For bronze, tool steel, steel and brass tubing, etc., the chasers 
should be ground so as to produce an angular hook. 



TAPPED DIE MILLED DIE 

Chasers Ground toward 
Center 



Chasers Ground with 
Angular Hook 


83 




THE 


STARRETT 


ROOK 


SCREW THREADS 

Screw thread standardization was first attempted through 
the efforts of Sir Joseph Whitworth in 1841 and of William 
Sellers in 1864. Whitworth’s work resulted in the Whitworth 
thread standard used in England and Sellers’ work culmi¬ 
nated in what was first known as the Franklin Institute 
standard and later the United States Standard thread. The 
United States Standard which has long been in use in the 
United States provides for a V-shaped thread with angles of 
60 degrees and with flat bottoms and tops equal to one- 
eighth the height of the triangle. This took the place of 
the old V-thread with sharp threads which were not as strong. 
The sharp thread has been obsolete for a good many years. 
The United States Standard also provided for a definite 
number of threads to the inch for each diameter. 

With the coming of the automobile, it was found desirable 
to use threads with a finer pitch than called for by the 
United States Standard and in the early days the Associa¬ 
tion of Licensed Automobile Manufacturers evolved a stand¬ 
ard of finer pitched threads known as the A. L. A.M. standard 
or sometimes the automobile standard. Later this stand¬ 
ard was placed in the custody of the Society of Automotive 
Engineers and it has since been known as the S. A. E. thread 
standard. 

Both the United States Standard and the S. A. E. standard * 
start with in* an d there is no provision for smaller diam¬ 
eters. Therefore, for small work machine screw threads are 
used. The American Society of Mechanical Engineers some 
years ago evolved a machine screw standard which was known 
as the A. S. M. E. standard and it provided for a definite num¬ 
ber of threads per inch for each size and also standardized the 
gage numbers of the screws. But the standard set was too 
fine for general use and the standard was not generally 
adhered to with the result that there has always been a 
good deal of confusion and multiplicity of threads in machine 
screw sizes. Another bad feature was that machine screw 
84 



FOR MOTOR MACHINISTS 


sizes ran up over J4 in! and overlapped the other sizes to a 
considerable extent. For instance a No. 14 screw is almost 
the same size as a 34 in* screw. 

In other industrial fields, other screw standards have been 
worked out and unfortunately these standards were not 
always alike. The result of all this was that when the 
United States entered the world war and all industries had 
to unite to turn out munitions, machinery and equipment, 
there was a great deal of confusion, a lack of real standardiza¬ 
tion and no authority for tolerances or even pitches. Accord¬ 
ingly, in 1918, Congress provided for the formation of a 
National Screw Thread Commission which would cover the 
ground in all the industries and which would set up stand¬ 
ards which could be adhered to in every shop in the country. 

The work bf this commission, in 1924, is not yet completed, 
but a great mass of duplication and confusion has already 
been removed. While the findings of the Commission so far 
have neither been adopted by Congress nor by any engineer¬ 
ing body, nevertheless, many manufacturers, tool makers 
and designers are following these.findings. 

The greatest accomplishment of the Commission is the 
establishment of a National Fine Thread Series and a 
National Coarse Thread Series. The Fine Thread Series is 
the same number of threads per inch as the S. A. E. standard 
from 34 i n * upward, and the inclusion in the same series of 
certain of the old machine screw sizes up to No. 12. The 
National Coarse Thread Series is the same as the United 
States Standard with the addition of machine screw sizes 
below J4in., the threads being coarser than in the other series. 
The S. A. E. Standard still includes an extra fine thread for 
airplane work which has not been included in the standards 
of the Commission. 

In addition to the standardization of threads, the Com¬ 
mission has standardized on tolerances, gages, etc. Already 
drill makers are marketing drills made the exactly correct 
size for certain taps and more of these will appear on the 

85 



THE 


STARRETT 


ROOK 


market as the standards become better known. In the 
National Coarse and Fine Thread Tables (See pages 97, 98), 
these special size drills will be found marked with an as¬ 
terisk (*). Several great automobile companies, notably the 
General Motors Company, have adopted the findings of the 
Commission as standard. 

In addition to the National Series Threads, Coarse and 
Fine, there are two other screw standards used on the auto* 
mobile. One of these is the standard pipe thread, used for 
gasoline and air connections, spark plugs, casting plugs, drain 
plugs, etc., and the stove bolt threads. Both of these stand¬ 
ards are listed in this volume. 

The screw threads commonly used in motor construction 
are as follows: The “V” thread, U. S. Standard, S. A. E. 
(Society of Automotive Engineers) Standard, Whitworth or 
British Standard, A. S. M. E. (American Society of Mechanical 
Engineers) Standard, Square, Acme, Worm, B. S. F. (British 
Standard Fine) Standard, B. A. S. (British Association Stand¬ 
ard) for very small screws, and the Metric. In addition, 
pipes and tubing are cut with American (Briggs’ “Standard”) 
Pipe Thread and British Standard Pipe Threads. The S. A.E. 
screw thread, formerly known as the A. L. A. M. thread, 
and the A. S. M. E. Standard are the same form of thread as 
the U. S. Standard, though what is commonly called the 
pitch, or number of threads to the inch, of the S. A. E. thread 
is much higher than that of the U. S. Standard thread. To 
these must now be added the new “National Series Threads” 
which will probably ultimately render obsolete all of the old 
threads. 

Figures 77 and 78 show the principal parts of a screw and 
thread and will aid in making clear the differences in the 
different types of threads in use. 

The angle of the thread (D) is the angle the sides of the 
thread make with each other, as shown in Fig. 77. The 
rake (E) is the angle between the side of thread and a line 
at right angles to the axis of the screw. The major or out- 

86 



FOR M Q T 0 R MACHINISTS 


side diameter (A) is the overall dimension, measuring to 
the outside of the threads. The minor, core or—as it is 
usually called—the root diameter (B) is the diameter of the 
screw at the base of the threads and is equivalent to the 
major diameter minus twice the depth of the thread. The 
pitch diameter (C) is the major diameter minus a single 
depth of thread. Pitch, see Fig. 78, is really the distance 
between two adjacent threads measured on a line parallel 
to the axis of the screw, though the term is often incorrectly 



Figs. 77-78—Principal Parts of a Screw—Principal Parts of a 
Thread 

used to indicate the number of threads to the inch. The 
proper name for “pitch” as meaning the number of threads 
to the inch, or the distance a nut will travel on a screw when 
the screw is given one turn, is lead. In a single thread screw, 
pitch and lead are equal, because the nut will move from 
one thread to the next with each turn of the screw, but in a 
double or triple thread screw the nut will move over two or 
three threads for each turn of the screw and in such screws 
the lead is two or three times the pitch. 

Double and triple thread screws*, often called multiple 
thread screws, are not commonly used in automotive prac- 
*See page 141, Vol. II, Starrett Books. 

87 





THE 


STARRETT 


BOOK 


tice. They may be used to advantage, however, on parts 
having thin walls or small diameters and which therefore 
will not stand a deep or coarse thread with a high lead. On 
such a part, where it is desirable for the nut or screw to 
move rapidly, a multiple thread will often solve the diffi¬ 
culty, the number of threads to the inch being greatly in¬ 
creased above normal, but are cut to only half the usual 
depth. For example, if a single thread with a 34 i n - lead 
and but a half or 34 in- pitch depth is cut on a small bolt 
and then another similar thread is cut between the threads 
already cut, the nut will move forward the full 34 i n - lead 
for each turn of the bolt, but will move over two threads 
in doing so. Such a thread would be called a “34 i n - lead 
by 34 i n - pitch, double”. 

The “V” Thread 

In the “V” thread the top or crest and the root are both 
theoretically sharp, but in actual practice there is formed a 
little flat of about l/25 inch. The angle is 60° and the depth 
(d) is .866 times the pitch (p), the pitch being obtained by 
dividing 1.000 by the number of threads to the inch. The 
formula for the “V” thread is as follows: 

P pitch ^ Threads per Inch 
d = depth = p x .86603. 



88 







FOR MOTOR MACHINISTS 


U. S. Standard Thread* 

The U. S. Standard is probably the thread most commonly 
used in machine shop practice and is an outgrowth of the 
“V” thread which has now been rendered almost obsolete, 
though it is still used as a pipe thread where it is known as 
the Briggs’ Standard. The disadvantages of the “V” thread 
were that it was an impossible thread to reproduce econom¬ 
ically because with the slightest wear on the thread cutting 



Fig. 80—Section of U, S. Standard Thread 

tools the crest and the root of the thread could not be made 
sharp. Consequently, when a “V” threaded nut and screw 
were assembled the bearing surfaces were only at the crest 
and root—instead of the sides—and a great tendency to 
unscrew was thereby developed. In the U. S. thread, where 
there is a flat at both the crest and the root of the thread, 
the sides become the bearing surface and the thread is not 
only much more economically produced, but the tendency 
to unscrew is overcome. 

The angle of the U. S. Standard thread is 60° as in the 
“V” thread. The width of the flats (f) is l / s the pitch. The 
depth (d) is .6495 times the pitch. The formula for the 
U. S. Standard thread is as follows: 

♦See pages 137-138, Vol. II, Starrett Books. 

89 



THE 


STARRETT 


BOOK 


p pitch Threads per Inch 

n = number of threads per inch 
6495 

d - depth - p X .6495 or—-— 
f = flat = ® 

o 

S. A. E. Standard Thread* 

The S. A. E. Standard thread is identical with what was 
known as the A. L. A. M. thread. In this standard the U. S. 
form of thread is used, the only difference being in the threads 
per inch for certain diameters. The finer pitch of the S. A. E. 
thread makes it particularly well adapted to automobile 
practice as it is less likely to work loose from vibration than 
is the comparatively coarse thread of the U. S. Standard. 
The formula of the S. A. E. thread is the same as for the U. S. 
Standard. 

Metric Threads f 

The metric thread standard is based on the U. S. Stand¬ 
ard, but to provide clearance at the root of the thread a 
radius not exceeding 1/16 of the height of the thread is 
recommended. There are really two metric standards, the 
French and what is called the International. The formula 
in each case is the same as for the U. S. Standard. 

Whitworth Thread Standard { 

The Whitworth thread, although used to some extent in 
locomotive practice in this country, is peculiar to English 
cars and machine parts of British origin. 

The angle in the Whitworth thread form is 55°, as com¬ 
pared with 60° in the U. S. Standard, and the crest and root 

*See page 134, Vol. II, Starrett Books. fSee page 136, Vol. II, Starrett Books. 

JSee page 139, Vol. II, Starrett Books. 

90 





FOR MOTOR MACHINISTS 



Fig. 80A—Section of a Whitworth Thread 

are rounded, rather than flattened, to a radius equal to .1373 
times the pitch. The formula is as follows: 

p pitch Q f 'pj ireac j s p er i nc k 

d = depth = p X .64033 
r = radius = p X .1373 


Square Thread Standard* 

The square thread is so made that the width between the 
threads and the depth of the thread are the same, and are 


Fig. 81—Section of a Square Thread 

equal to 1/2 the pitch. There is no recognized standard for 
this thread and it is being rapidly superseded by the Acme 
thread which is easier to cut. While theoretically, a square 

*See page 135, Vol. II, Starrett Books. 

91 






THE 


STARR ETT 


BOOK 


thread, as its name implies, and as is shown in Fig. 81, has 
straight sided threads, in actual practice it is customary to 
leave a slight amount of rake—2° to 5°—so the sides of the 
thread are not exactly parallel, or at right angles to the axis 
of the screws. 

Acme Standard Thread* / 

The Acme thread was adapted from the worm thread, 
and was introduced to overcome the disadvantages and diffi- 
ficulties in cutting the square thread. It is a little shallower 



Fig. 82—Section of Acme Thread 

than the worm thread, but the same depth as the square 
thread and much stronger than the latter. 

The angle of the Acme thread is 29°, as shown in Fig. 82. 
The depth of the thread is V 2 the pitch plus .010 in. for clear¬ 
ance. The root diameter of the screw is the nominal diam¬ 
eter of the screw less the pitch plus .020 in., the nut for this 
thread being made .020 in. oversize. The formulae for the 
Acme standard thread are as follows: 

Width of Point of Tool for Screw or Tap Thread 


No. of Threads per Inch 

*See page 136, Vol. II, Starrett Books. 

92 








FOR MOTOR MACHINISTS 


Width of Screw or Nut Thread 

_.3707_ 

No. of Threads per Inch 

Diameter of Tap = Diameter of Screw +.020 

Root Diameter of Tap or Screw 

= Diameter of Screw— -r—r + .020} 

\JNo. 01 1 breads per Inch / 

= p 4- .020 

Depth of Thread 

= 2 X No. of Threads per Inch + -01 ° = ^ P + ' 01 ° 

The Acme standard has no standard number of threads 
per inch for certain diameters as have all other standards 
and should, therefore, never be specified as a “ ^ or 1 in., 
etc., Acme”. To identify an Acme screw the pitch diameter 
or the number of threads per inch should be given. 


93 






THE 


STARRETT 


ROOK 


TAP DRILL SIZES 

75% DEPTH OF THREAD 

A bolt inserted in an ordinary nut which has only one-half 
of a full depth of thread, will break before stripping the 
thread. Also, a full depth of thread, while very difficult to 
obtain, is only about 5% stronger than a 75% depth. 

These tables give the exact size of the hole, expressed in 
decimals, that will produce a 75% depth of thread and also 
the nearest regular stock drill to this size. Holes produced 
by these drills are close enough for any commercial tapping. 

.974 

Diam. of Tap — ^——:-=—r =Diam. of Hole 

JNo. Ihreads per Inch 


Tap Drill Sizes—75 Per Cent Depth Thread 
Machine Screw Threads 


Tap 

Size 

Threads 
per In. 

Diam. 

Hole 

l| 

Tap 

Size 

Threads 
per In. 

Diam. 

Hole 

Drill 

Tap 

Size 

Threads 
per In. 

Diam. 

Hole 

Drill 

0 

*80 

.048 

% 

7 

*36 

. 124 

H 

16 

*22 

.224 

2 

1 

*72 

.060 

53 

7 

32 

. 121 

31 

16 

20 

.219 


1 

64 

.058 

53 

7 

30 

. 119 

31 

16 

18 

.214 

3 

2 

*64 

.071 

50 

8 

*36 

. 137 

29 

18 

*20 

.245 

D 

2 

56 

.069 

51 

8 

32 

. 134 

29 

18 

18 

.240 

B 

3 

*56 

.082 

46 

8 

30 

. 132 

30 

20 

*20 

.271 

I 

3 

48 

.079 

47 

9 

*32 

. 147 

26 

20 

18 

.266 


4 

*48 

.092 

42 

9 

30 

. 145 

27 

22 

*18 

.292 

L 

4 

40 

.088 

44 

9 

24 

. 136 

29 

22 

16 

.285 

% 

4 

36 

.085 

44 

10 

32 

. 160 

21 

24 

18 

.318 

6 

5 

*44 

. 103 

38 

10 

*30 

. 158 

22 

24 

*16 

.311 

54 

5 

40 

. 101 

39 

10 

24 

. 149 

26 

26 

*16 

.337 

R 

5 

36 

.098 

40 

12 

*28 

. 181 

15 

26 

14 

.328 


6 

*40 

. 114 

33 

12 

24 

. 175 

17 

28 

16 

.363 


6 

36 

. Ill 

34 

14 

*24 

.201 

7 

28 

*14 

.354 

T 

6 

32 

. 108 

36 

14 

20 

. 193 

10 

30 

16 

.389 










30 

*14 

.380 

V 


*A. S. M. E. Standard. 


94 




























FOR MOTOR MACHINISTS 


Tap Drill Sizes—75 Per Gent Depth Thread 
Special and Standard Threads 


Tap 

Size 

Threads 
per In. 

Diam. 

Hole 

Drill 

Tap 

Size 

Threads 

per In. 

Diam. 

Hole 

Drill 

Tap 

Size 

Threads 

per In. 

Diam. 

Hole 

Drill 

'A 

72 

.049 

3 4 

X 

32 

.220 

X 2 

X 

*14 

.805 

'Xe 

!4 

64 

.047 

% 

X 

*28 

.215 

3 

X 

12 

.794 

5 14 

Xe 

60 

.046 

56 

X 

27 

.214 

3 

tx 

9 

. 767 

*Xi 

X 

72 

.065 

52 

X 

24 

.209 

4 

'Xe 

12 

.856 

3 Xi 


64 

.063 

Xe 

tx 

20 

.201 

8 

'Xe 

9 

.829 

5 Xi 

% 

60 

.062 

Xe 

Xe 

32 

.282 

% 

1 

27 

.964 

S, A 

% 

56 

.061 

53 

Xe 

27 

.276 

J 

1 

*14 

.930 

'Xe 

% 

60 

.077 

Xi 

Xe 

*24 

.272 

% 

1 

12 

.919 

59 A 

% 

56 

.076 

48 

Xe 

20 

.264 

17 A 

1-1 

8 

.878 

X 

% 

50 

.074 

49 

tXe 

18 

.258 

F 

1 Xe 

8 

.941 

'Xe 

'& 

48 

.073 

49 

X 

27 

.339 

R 

1 X 

*12 

1.044 

1 Xi 


56 

.092 

42 

X 

*24 

.334 

Q 

ti X 

7 

.986 


7 44 

50 

.090 

43 

X 

20 

.326 

2 14 

1 X 

7 

1.048 

1 % 

% 

48 

.089 

43 

tx 

16 

.314 

Xe 

1 x 

*12 

1. 169 

1'Xi 

'A 

48 

. 105 

36 

Xe 

27 

.401 

Y 

ti X 

7 

1. Ill 

1 % 

X 

40 

. 101 

38 

Xe 

24 

.397 

X 

1 X 

7 

1. 173 

VXi 

X 

36 

.098 

40 

Xe 

*20 

.389 

2 X 

1 

12 

1. 294 

V% 

X 

32 

.095 

X 2 

tXe 

14 

.368 

u 

l X 

6 

1. 213 

1 'Xe 

^4 

40 

. 116 

32 

X 

27 

.464 

'X 2 

l 'A 

*12 

1.419 

i 27 4 

% 

36 

. 114 

33 

X 

24 

.460 

29 4 

tl 'A 

6 

1.338 


X 4 

32 

. 110 

35 

X 

*20 

.451 

29 -4 

1 X 

5'A 

1.448 

129> 

X 2 

40 

. 132 

30 

tx 

13 

.425 

27 4 

ti X 

5 

1. 555 

1H4 

Xi 

36 

. 129 

30 

X 

12 

.419 

27 A 

1 X 

5 

1. 680 

I'Xe 

Xi 

32 

. 126 

X 

Xe 

27 

.526 

'X 2 

t2 

4'A 

1. 783 

1 2 X2 


36 

. 145 

27 

Xe 

*18 

. 508 

S X 

2 X 

4'A 

1. 909 

1 2 X2 


32 

. 141 

% 

tXe 

12 

.481 

S X 

2 ¥> 

4 X 

2. 034 

2 X 2 

Xe 

36 

. 161 

20 

X 

27 

.589 

'X 2 

2 x 

4 

2. 131 

2 X 

Xe 

32 

. 157 

22 

X 

*18 

.571 

37 4 

t2 'A 

4 

2. 256 

2X 

Xe 

30 

. 155 

23 

X 

12 

.544 

83 4 

2X 

4 

2. 381 

2 X 

iji 

24 

. 147 

26 

tx 

11 

.536 

'X 2 

t2 x 

4 

2. 506 

2 x 


32 

. 173 

17 

'Xe 

16 

.627 

X 

2 Vs 

S'A 

2. 597 

2 l9 /?2 


30 

. 171 

"A 

'Xe 

11 

.599 

'% 

f3 w 

3 X 

2. 722 

2 X 

u 4i 

24 

. 163 

20 

M 

27 

. 714 

2i A 

3 'A 

3 X 

2. 847 

2 2 X2 

X 2 

32 

. 188 

12 

% 

*16 

.689 

'Xe 

SX 

SA 

2. 972 

2*X2 

% 

28 

. 184 

13 

H 

12 

.669 


3 X 

sx 

3. 075 

3 We 

X 2 

24 

. 178 

16 

tx 

10 

.653 

2 % 

S'A 

sx 

3. 200 

3 Xe 


32 

.204 

6 

'Xe 

12 

.731 

Xu 

3 X 

sx 

3. 325 

3 Xe 

l X\ 

28 

.200 

8 

'Xe 

10 

.715 

2 X,1 

3 X 

3 

3.425 

3 Xe 

l xl 

24 

. 194 

10 

x 

27 

.839 

27 A 

3X 

3 

3. 550 

3 Xe 





X 

18 

.821 

53 ^- 

4 

3 

3. 675 

S'Xe 


*s. A. E. Standard. tU. S. Standard. 


95 





























THE 


STARRETT 


ROOK 


UNITED STATES STANDARD SCREW THREADS 
(Sizes above 3 inches are U. S. S. Form) 


Diameter 

Threads 

Per Inch 

Diameter 
at Root 
of Thread 

Diameter of 
Tap Drill 

Sectional Area 
in Square Inches 

Nuts and Bolt Heads* 

Across 

Hats, 

Square 

and 

Hex. 

Across Corners a 

Thick¬ 

ness, 

Bolt 

Head 

Solid 

Bolt 

At Root 
of Thread 

Hexagon 

Square 

X 

20 

0.1850 

No. 8 

0.0491 

0.0269 

X 

0.5774 

0. 7071 

X 

5 /16 

18 

0. 2403 

X 

0. 0767 

0. 0459 


0.6856 

0.8397 

19 ^4 

X 

16 

0. 2938 

% 

0. 1104 

0. 0677 

1 Ws 

0.7939 

0. 9723 

• n /6 

14 

14 

0.3447 


0. 1503 

0. 0933 

2 X 2 

0.9021 

1.1049 

2 34 

X 

13 

0. 4001 

=% 

0.1964 

0.1257 

X 

1.0104 

1.2374 

7 Tg 

% 

12 

0. 4542 

3 44 

0.2485 

0. 1620 

S ’^2 

1.1186 

1.3700 

3 14 

X 

11 

%. 5069 

17 4 2 

0.3068 

0. 2018 

114 

1.2269 

1. 5026 


% 

10 

0.6201 

2 42 

0.4418 

0. 3024 

IX 

1.4434 

1.7678 

X 

X 

9 

0. 7307 

4 4* 

0.6013 

0.4230 

114 

1.6600 

2. 0329 

23 4> 

1 

8 

0.8376 

X 

0.7854 

0.5510 

IX 

1.8764 

2. 29S1 

13 d6 

IX 

7 

0.9394 

63 4 

0. 9940 

0.6931 

i 13 4 

2. 0929 

2. 5633 


IX 

7 

1.0644 

114 

1.2272 

0.8898 

2 

2. 3094 

2.8284 

1 

1 X 

6 

1.2835 

1‘4 2 

1.7672 

1.2938 

2 % 

2.7424 

3.3588 

m 

m 

5 

1.4902 

i 3 44 

2.4053 

1.7454 

2 M 

3.1754 

3.8891 

m • 

2 

4J4 

1.7113 

i 4 % 

3.1416 

2.3000 

334 

3. 6084 

4.4194 

1 % 

2H 

434 

1.9613 

242 

3.9761 

3.0212 

m 

4.0414 

4.9498 

IX 

2^2 

4 

2.1752 

2 M 

4.9087 

3.7161 


4.4745 

5.4801 

1 13 4 

2% 

4 

2.4252 

24 

5. 9396 

4.6180 

4K 

4.9075 

6. 0104 

2 ^ 

3 

34 

r2. 675 

2M 

7.0686 

5.520 

4x 

5.3405 

6.5407 

2% 

3 A 

34 

2. 8788 

2 ! 5 /16 

8.2958 

6. 5090 

5 

5.7735 

7.0711 

2X 

34 

34 

3.1003 

3 “4 

9.6211 

7.5492 

5 X 

6.2065 

7.6014 

2 U/6 

3U 

3 

3.3170 

34 

11.045 

8.6414 

5M 

6.6395 

8.1317 

2X 

4 

3 

3.5670 

34 

12.566 

9.9930 

6X 

7.0725 

8.6621 

3% 

4 k 

2% 

3. 7982 

3 27 4 

14.186 

11.330 

6 X 

7.5055 

9.1924 

3X 

4 4 

2 >4 

4.0276 

m 

15. 904 

12. 740 

VA 

7.9386 

9. 7227 

3!4 

4 X 

2 4 

4.2551 

44 

17.721 

14.220 

7M 

8.3716 

10. 253 

354 

5 

2 4 

4.4804 

44 

19.635 

15.766 

m 

8.8046 

10.783 

3 13 /6 

5h 

2Vc 

4.7304 

4 13 4 

21.64S 

17.575 

8 

9.2376 

11.314 

4 

5H 

2 4 

4.9530 

542 

23. 758 

19. 268 

8^ 

9.6706 

11. 844 

414 

5M 

2'4 

5.2030 

542 

25. 967 

21.262 

8 X 

10.104 

12.374 

4X 

6 

2 4 

5.4226 

5.4 

28.274 

23. 094 

9 34 

10. 537 

12.905 

4X6 


*Thickness of nut equals diameter of bolt. 

a. In practice these are a trifle less than shown, because the corners are slightly 
rounded. 


96 




















FOR MOTOR MACHINISTS 


NATIONAL COARSE THREAD SERIES 


Diam¬ 

eter 

Thre’ds 

Major 

Diam¬ 

eter 

Body 

Drill 

Hole to 
Tap 83% 
Thread 

Hole to 
Tap 75% 
Thread 

Recom¬ 
mended 
Tap Drill 
(75-80%) 

1 

64 

.073 

49 

.0561 

. 0578 

.0575* 

2 

56 

.086 

44 

.0667 

.0686 

.0682* 

3 

48 

.099 

39 

.0764 

.0787 

% 

4 

40 

. 112 

33 

.0849 

.0876 

44 

5 

40 

. 125 

30 

.0979 

.1006 

39 

6 

32 

. 138 

28 

. 1042 

. 1076 

36 

8 

32 

.164 

19 

. 1302 

.1336 

.1324* 

10 

24 

. 190 

11 

. 1449 

. 1494 

26 

12 

24 

.216 

2 

. 1709 

. 1754 

17 

H 

20 

.2500 

K 

. 1959 

.2013 

8 

% 

18 

.3125 

% 

.2524 

.2584 

F 

Vs 

16 

.3750 

y 8 

.3073 

.3141 

% 

7 A> 

14 

.4375 

14 

.3602 

.3679 

U 

y 2 

13 

.5000 

A 

.4167 

.4251 

27 A 

% 

12 

.5625 

% 

.4723 

.4813 

.4776* 

y 8 

11 

.6250 

y 8 

.5266 

.5364 

17 ^ 

% 

10 

.7500 

k 

.6417 

.6526 

.6480* 

A 

9 

.9750 

y 8 

.7547 

.7667 

.7615* 

i 

8 

1.0000 

i 

.8647 

.8782 

.8723* 

iy 8 

7 

1.1250 

i y 8 

.9704 

.9858 

.9789* 

1M 

7 

1.2500 

m 

1.0954 

1.1108 

1% 

i h 

6 

1. 5000 

l'A 

1.3196 

1.3376 

l 21 4 

1M 

5 

1.7500 

IK 

1.5335 

1.5551 

1. 5453* 

2 

4 ^ 

2.0000 

2 

1. 7594 

1.7835 

l 25 ^ 

2H 

4 H 

2.2500 

2 K 

2. 0094 

2.0335 

2.0225* 

2A 

4 

2.5000 

2A 

2.2294 

2.2564 

2 M 

2% 

4 

2.7500 

2 K 

2.4794 

2.5064 

2.4939* 

3 

4 

3.0000 

3 

2. 7294 

2.7564 

2.7439* 


♦These are standard stock drill sizes and are readily obtainable. 

97 


Nearest. Other 
Tap Drill 


53 (67%) 
51 (82%) 
47 (76%) 
43 (71%) 
38 (72%) 


29 (69%) 
25 (75%) 
16 (72%) 
7 (75%) 
Vi (82%) 


*Ut (82%) 


s Wt (72%) 


2 !4 (72%) 
(76%) 
A (77%) 
(76%) 


1* 14 (72%) 
1 S5 A (78%) 
(81%) 
214 (76%) 
2 15 4 (82%) 
2 A (77%) 
2H (77%) 





















THE 


STARRETT 


BOOK 


NATIONAL FINE THREAD SERIES 


Diam¬ 

eter 

Thre’ds 

Major 

Diam¬ 

eter 

Body 

Drill 

Hole to 
Tap 83% 
Thread 

Hole to 
Tap 75% 
Thread 

Recom¬ 
mended 
Tap Drill 
(75-80%) 

Nearest Other 
Tap Drill 

0 

80 

.060 

52 

.0465 

. 0478 

3 U 

56 (83%) 

1 

72 

.073 

49 

.0580 

. 0595 

53 


2 

64 

.086 

44 

. 0691 

. 0708 

50 


3 

56 

.099 

39 

.0797 

. 0816 

46 

45 (73%) 

4 

48 

. 112 

33 

.0894 

.0917 

.0911* 

42 (68%) 

5 

44 

. 125 

30 

. 1004 

. 1029 

38 

37 (71%) 

6 

40 

. 138 

28 

. 1109 

. .1136 

33 

34 (83%) 

8 

36 

. 164 

19 

. 1339 

. 1369 

29 


10 

32 

. 190 

11 

. 1562 

. 1596 

21 

22 (81%) 

12 

28 

.216 

2 

. 1773 

. 1812 

15 

14 (73%) 

K 

28 

.2500 

K 

.2113 

.2152 

3 


% 

24 

.3125 

% 

.2674 

.2719 

.2703* 

17 4t (100%) 

K 

24 

.3750 

X 

.3299 

.3344 

Q 

(ioo%) 

K« 

20 

.4375 

Ke 

.3834 

.3888 

W 

(72%) 

K 

20 

.5000 

X 

.4459 

.4513 

.4492* 

29 ^ (72%) 

% 

18 

.5625 

% 

.5024 

.5084 

.5062* 

3 % (65%) 

H 

18 

.6250 

X 

.5649 

.5709 

.5687* 

37 A (65%) 

X 

16 

.7500 

K 

.6823 

.6891 



7 A 

14 

.8750 

K 

.7977 

.8054 

.8024* 

13 A (67%) 

l 

14 

1.0000 

l 

.9227 

.9304 

.9274* 

15 -4 (67%) 

IK 

12 

1.1250 

IK 

1.0348 

1.0438 

1.0401* 

(72%) 

IK 

12 

1.2500 

IK 

1.1598 

1. 1688 

1.1651* 

l 11 ^ (72%) 

IK 

12 

1. 5000 

IK 

1.4098 

1.4188 

1.4153* 

1 27 A (72%) 

IK 

12 

1.7500 

IK 

1. 6598 

1.6688 

1. 6653* 

l i3 A (72%) 

2 

12 

2.0000 

2 

1.9098 

1.9188 

1.9153* 

1 5 % (72%) 

2K 

12 

2.2500 

2K 

2.1532 

2.1687 

2K 2 

— 

2K 

12 

2.5000 

2K 

2.4032 

2.4187 

2^2 


2K 

12 

2.7500 

2K 

2.6532 

2.6687 

2 2 K> 


3 

10 

3.0000 

3 

2.8919 

2.9027 

2 i7 A 



*These are standard stock drill sizes and are readily obtainable. 

98 

























FOR M OTOR MACHINISTS 


HOW TO USE THICKNESS GAGES 



Fig. 83 —Thickness Gage 


One of the most useful and indispensable tools in an auto¬ 
mobile repair shop, and at the same time one of the least 
expensive, is the thickness gage. See Fig. 83. This tool is 
of great use in making inspections of various parts of the 
car for wear, in eliminating guesswork and—when the 
necessity is imperative—it can be made to approximate the 
work of a number of other and much more expensive tools. 
Thickness gages consist of a varying number of metal leaves 
of different thicknesses fastened together in a convenient 
holder in such a manner that any combination of them may 
be made. The thickness of each leaf is plainly indicated and, 

99 










THE 


STARRETT 


ROOK 


having found a combination of leaves that just fills the space 
to be measured, the sum of the thicknesses of the various 
leaves used indicates the width or thickness of the space. 
Again, it may be desired that a gap—as in a spark plug— 
shall be a certain amount. In such a case a leaf or leaves 
having the desired thickness is selected and the gap made 
to conform to it. 

Spacing gaps in spark plugs is perhaps the commonest use 
of thickness gages in garage and repair shop work and is far 
too often a piece of guesswork. In most ignition systems, 
the proper width for a spark gap is 1/32 of an inch. Refer¬ 
ence to a decimal equivalent table shows that 1/32 in. is 
.031 in.—a thickness easily determined on a thickness gage 
made for the automobile trade by placing the proper leaves 
together. 

Setting Contact Breaker Points 

Another motor—or rather ignition—part which calls for 
the use of a thickness gage if good work is to be done, is the 
contact breaker. Here the gap varies from .010 to .015, 



Fig. 84— Setting Spark Plug Fig. 85— Setting Breaker Contact 
Gaps Points 


100 






FOR MOTOR MACHINISTS 


according to the type of ignition system, and the difference 
of a very few thousandths of an inch determines the efficiency 
of the motor. Never attempt to set contact breaker points 
without using a thickness gage. 

Adjusting Tappets 

Adjusting tappets or push rods is another common use for 
thickness gages. Tappets are usually set to give a clearance 
between the push rod and tappet, or between the rocker arm 
and the end of the valve stem, of from .002 to .005 in.— 
according to the make of motor—when the engine is hot. 
Pieces of paper are often used for this purpose, but it should 
be realized that paper thicknesses range from .001 to .020 
inch and that such a method is little more than guesswork. 
Manufacturers’ recommendations, as regards the amount 
of clearance, should be closely followed and a thickness gage 
invariably used. 

Pistons and Piston Rings 

Thickness gages may also be used, when the proper tools 
are not available—cylinder gage or inside micrometer—in 
fitting new or oversize pistons. When the work has to be 
done with a thickness gage, the old piston should be placed 
in the bore and the blades of the gage tried successively until 











THE STARRETT ROOK 


one—or a combination—is found that will just enter between 
the piston and the cylinder wall. The piston is then re¬ 
moved, measured with an outside micrometer and the thick¬ 
ness of the gage blade added. The result indicates the actual 
diameter of the cylinder bore. A thickness gage can also be 
of some assistance in determining if, and how much, a cylinder 
is out of round, though to do a satisfactory job a cylinder 
gage should be employed. In using a thickness gage for 
this work, merely insert a new and true piston in the cylinder 
and test the clearance—using blades of different thicknesses 
if necessary—all around the circumference of the piston. 

A thickness, or feeler gage as it is sometimes called, may 
be used to check the clearance of pistons and cylinders before 
assembly, even though they have been properly measured 
with micrometers. 

Thickness gages should be used in checking the gap in 
both step and diagonal joint piston rings. The usual allow¬ 
ance for expansion of the ring by the heat of the motor is 
about .001 in. per inch of bore. Patent or compound rings, 
etc., are made with correct clearances by the manufacturer 
and no fitting is necessary. 

Shim Fitting 

Thickness gages should be used also in all worn calling for 
fitting of shims. In replacing or scraping in connecting rod, 
crank or camshaft bearings, work on chassis or running gear, 
steering wheel spindles, and springs and shackle bolts, thick¬ 
ness gages can be used to determine beforehand the actual 
thickness of shim required. In the case of shaft bearings 
that have been scraped or lapped, put on the cap without 
any shims, draw up approximately tight and then use the 
thickness gage between the bearing and the shaft to find the 
total amount of shim required. Divide that by two to get 
the shim thickness for each side. Wherever shims are to 
be used, a thickness gage will save a great amount of trouble 
as well as considerable cut-and-try-work and material. 

102 



F O R MOT OR MACHINISTS 


Gear Meshing 

Various gears in the car are supposed to run with various 
amount of backlash depending on their construction, opera¬ 
tion and work. It is possible—with the exception of ex¬ 
tremely small gears—to mesh gears very exactly by using a 
feeler gage to determine the backlash. 

GAGING CYLINDER BORES 

A machinist in any motor repair or service shop should 
be supplied with the necessary tools to enable him to test 
and gage cylinder bores accurately in order to determine if 
and how much they are tapered, out of round or scored. To 
do the job most efficiently and in a manner that will indicate 
the exact condition of the cylinder to even the most ignorant 
car owner, he should have a cylinder gage (Fig. 87) and out¬ 
side micrometer for transferring measurements from the 
gage (Fig. 88). 

A gage, such as is shown in Fig. 87, consists of a sled on 
which are two line contact points that are at all times in 
alignment with the walls of the cylinder. These hardened 
contact points record taper, eccentricity, scoring, e'tc., by 
the position or movement of the hand on the dial when the 
gage is moved up or down or rotated in the cylinder bore. 
The dial is graduated to read plus and minus by .001 in., 
and provision is made for gaging cylinders of any diameter 
between 2^ in. and 6 in. A double spring action makes 
the gage self-centering and absolutely non-collapsible. 

The method of using the gage is indicated in Fig. 89. 
First place the sled against the bore of the cylinder, then 
set the adjustable contact point out over the edge of the 
bore so when the gage is set down in the cylinder the ten¬ 
sion on the springs will show that the hand on the dial has 
been forced to the minus side 40 or 50 thousandths, at 
least enough so that both contact points are forced against 
the walls of the cylinder. Turn the knurled rim of the dial 
103 



THE STARRETT BOOK 


so that the hand registers at 0 and move the 
gage up and down to test for taper, rotating it 
to check up for out-of-round or scored cylinders. 
Be sure to draw out the rod carrying contact 
point far enough to insure the self-centering 
action of the springs is brought into play. 
After the variation has been noted, the mean 
diameter of the cylinder in inches and thou¬ 
sandths of an inch is found by transferring to 
an outside micrometer. Slant the gage when 
removing it from the cylinder. Do not snap it 
out. This method has not only the advantage 
of being absolutely accurate from the mechanics’ 
standpoint — as well as being exceedingly sim¬ 
ple and quick—but also, when reboring, re¬ 
grinding or honing, or when new pistons are 
necessary, leaves nothing to the imagination or 
faith of the car owner. He can see for himself 
the condition of the cylinders to the one- 
thousandth part of an inch. 

Another method of gaging and testing cylinder 
bores, in which, however, considerable depend¬ 
ence must be placed on “feel”, is to use an inside 
micrometer. (See pages 18 
and 19.) 

The indicating and oper¬ 
ating parts of this instrument 
are very similar to those of 
the outside micrometer pre¬ 
viously described and the 
method of reading is the 
same. It should be noted, 
however, that the inside 
micrometer obviously has no 
zero, the minimum being the 
length of the rod inserted 

104 



ig. 87—Cylinder Gage 
(Starrett) 












FOR MOTOR MACHINISTS 


Fig. 88—Transferring Cylinder Measurement from Cylinder 
Gage to Outside Micrometer 



in the micrometer head, as 2.000, 3.000 or 4.000, etc., inches. 
The rods, just mentioned, remain fixed in the sleeve of the 


micrometer head and replace 
crometer. Otherwise, except 
are the same. 

The anvil is placed on the 
outer end of the thimble 
and when the micrometer is 
opened is forced out until the 
end of the rod comes in con¬ 
tact with one side of the 
cylinder wall and the anvil 
with the other. The dis¬ 
tance between the two is the 
bore of the cylinder and is 
indicated by the graduations 
on the sleeve and thimble. 

When using the tool, the 
micrometer is held in one 
hand, the end of the rod 
brought into contact with 
one side of the cylinder wall 
and the thimble turned by 
the fingers of the other hand, 
opening the micrometer until 


the spindle of the outside mi- 
for physical form, the tools 



Fig. 89—Dial Test Indicator 
Used on Cylinder Regrind¬ 
ing Job 


105 














THE 


STARRETT 


ROOK 


the anvil “feels” the opposite wall. Swinging the tool in an 
arc about the axis of the cylinder determines whether or 
not the bore is out of round, while by raising or lowering the 
micrometer, the cylinder may be tested for taper. In all cases, 



Fig. 90 —Telescoping Gage—Starrett 


the accuracy of the measurement depends largely upon the 
“feel”. For measuring long bores, or holes too small to per¬ 
mit the insertion of the hand, an extension handle is provided. 

Another tool used in a similar manner to measure cylinder 
bores, and which is more nearly automatic in its action — 
though it is not direct reading and, therefore, requires the 
use of an outside micrometer — is the telescoping gage. 

106 













FOR MOTOR MACHINISTS 


This tool consists of a steel rod sliding in a sleeve, from 
which it is automatically forced outward by a light spring, 
and which may be locked at any point by a slight turn of the 
knurled screw in the extension handle which serves to lower 
the gage into the hole to be measured. To use the tool, all 
that is necessary is to compress the telescoping head and lock 
it in the sleeve by turning the screw in the handle. After 
inserting the tool in the cylinder bore, release the telescoping 
head or plunger. A spring under or behind the plunger forces 
it outward until it comes in contact with the opposite side of 
the cylinder wall. After turning the screw again to lock the 
plunger, withdraw the tool and transfer the measurements to 
an outside micrometer as was done with the cylinder gage. 

Both the inside micrometer and the telescope gage can be 
used in fitting pistons to cylinder bores as well as for fitting 
cylinder bores to pistons. When it is desired to fit a piston to 
a cylinder, it is necessary only to caliper the piston with an 
ordinary pair of outside calipers and transfer the measurement 
either to an inside micrometer — where it can be read direct 
— or to a telescoping gage and thence to an outside micro¬ 
meter for direct reading when opportunity arises or at the 
convenience of the machinist. However, for rapidly and 
accurately determining the exact condition of cylinders, a 
cylinder gage, such as was shown in Fig. 87, should be used. 

CYLINDER GRINDING 

Before starting to rebore or grind cylinders, the greatest 
pains must be taken to make sure that the cylinder bore is 
at right angles with the base of the block. To do this, the 
block should be mounted on angle irons bolted to the table 
of a good cylinder regrinding machine. In the spindle of 
the grinder mount a dial test indicator (See Fig. 102, page 
137) and bring the point of the indicator in contact with the 
face of the block, setting the dial at zero. Then move the 
cross slide until the entire length of the block face has been 
traversed by the indicator point, which should read at zero 
107 



THE 


STARRETT 


BOOK 


throughout. If there is any variation it indicates that the 
block is not properly set, and must be readjusted. 

The next operation is to examine the cylinder bores, the 
cylinder with the greatest amount of wear being ground 
first, as it determines the size to which the other cylinders are 
to be ground. The first step is to measure or “mike” with 
an inside micrometer the cylinder showing the least amount 
of wear—usually the one at the rear of the block. This 
determines whether or not the cylinders have been previously 
reground or rebored, and, if not, it indicates the original 
diameter of the bore within .001 and .002 inch. Having 
determined the original bore of the cylinders and set an 
outside micrometer to this dimension, the pistons should be 
“miked” to determine their condition. 

The condition of each cylinder bore is the next thing to 
be ascertained and to do this each should be tested with a 
dial cylinder gage set so that it would have read zero in the 
original bore. The information gained from the use of the 
cylinder gage enables the machinist to know exactly how 
much to remove from each bore to straighten it up and bring 
it into round and also what diameter oversize pistons and 
rings are needed. As has already been said, tho cylinder 
which shows the greatest wear determines the size to which 
the others are to be ground and a standard oversize should 
always be selected. According to S. A. E. practices, there 
are four standard oversizes for cylinder bores, as follows. 

1st Oversize = d + .010 in. 

2nd Oversize = d + .020 in. 

3rd Oversize — d+ .030 in. 

4th Oversize = d + .040 in. 

d = orignal diameter of cylinder 

The grinding and regrinding of automobile cylinders is 
so extensive that a number of machines have been developed 
especially for this purpose. While the machines differ in 
details, the principles of all of them are about the same, 

108 



FOR MOTOR MACHINISTS 


The cylinder block to be ground is mounted on a jig which 
holds it in exact position after the workman has properly 
lined it up. The grinding wheel is quite small in diameter, 
about O /2 or 2 in., and revolves at a very high speed, some, 
3000 or 4000 R.P.M., depending on the diameter. The shaft 
of the wheel is mounted in a sort of eccentric whose distance 
off center is adjustable by means of a control lever. This 
eccentric revolves also, but at a very much slower rate than 
the wheel. By setting the machine up properly, the wheel 
is made to slowly turn around and revolve at the same time, 
its surface just touching all parts of the diameter of the cyl¬ 
inder. The wheel is fed into the cylinder bore automatically, 
the feed being adjustable. 

It is usual to take several “cuts” or bites in refinishing a 
cylinder and these may vary anywhere from .001 to .006 in. 
each. The first bite is light so that the alignment of the 
cylinder can be observed and checked. The roughing cuts 
are heavy and the final finishing cut is about .001 or .002 in. 

It might be thought that the 
cylinder refinished by the grinding 
method would be tapered owing 
to the fact that the wheel wears 
down as it grinds. This wear, how¬ 
ever, is very slight and the finish¬ 
ing cut is made both in and out so 
that any difference in diameter is 
' scarcely distinguishable with the 
most delicate measuring instru¬ 
ments. A diagram of the motions 
of the cylinder grinder is shown 
in Fig. 91A. 

While the standard oversizes are 
10, 20, 30, and 40 thousandths 
inch, many grinders work in between these standards if 
the cylinder can be brought true with less grinding. It 
is not absolutely necessary that all the cylinders measure 

109 



Fig. 91A —Diagram or' the 
Motions of the Cylinder 
Grinder 



THE 


STARRETT 


BOOK 


the same exact diameter because the very slight increase in 
combustion space is more than offset by many other inequal- 
ties in the engine such as uneven cylinder head castings, 
uneven cam contours and unequal valve tappet clearances. 

LAPPING CYLINDERS 

Where cylinders are not more than .003 in. out of round 
or tapered to that extent, they can be trued up by lapping. 
The process of lapping is quite old and is performed with 
a piston which is slit with a hacksaw as shown in Fig. 91B. 
The handle is moved up and down and at the same time given 
a spiral motion. At each stroke the position of the handle 
is advanced slightly so that the lap gradually turns around 
in the cylinder. This is to distribute the grinding uniformly 
around the cylinder and prevent rifling or wearing a spiral 
groove in one spot. The lap is kept charged with fine grind¬ 
ing compound mixed to the proper consistency with oil. The 
lap is kept operating until measurements with the inside mi¬ 
crometer or dial gage show that the bore is true as to round¬ 
ness and lack of taper. The lapping compound is then, 
thoroughly washed out of the bore with gasoline and the new 
piston rings fitted. It is sometimes necessary to lap the 
new piston lightly in the cylinder to finish the fitting. 

Lapping to remove a considerable quantity of metal is a 
slow and laborious job and it takes from 8 to 12 hours to 
properly lap a four-cylinder engine, depending upon how 
far out of true the cylinders were to begin with. There are 
on the market several electrical and mechanical lapping 
machines which will do the work just as well as it can be 
done by hand and in a much shorter time. 

CYLINDER HONING 

Cylinder Honing is a cylinder finishing process that has 
come into rather general use quite recently. The hone 
consists of a steel frame or cradle which supports four grind¬ 
ing stones which are pressed against the cylinder walls by 
110 



FOR MOTOR MACHINISTS 


springs. A suitable lubricant is used and the hone is revolved 
in the cylinder, being moved up and down at the same time, 
somewhat after the manner of the cylinder lap. 

Hones are generally provided with two or more grades 
of stones for fine or coarse honing and very often the hone is 
revolved by means of a portable electric drill although a 
drill press can be used if the cylinder block *s off the engine. 

The cylinder hone can be used for truing up cylinders that 
are out of round within certain limits and also cylinders that 
are tapered or bell mouthed within certain limits. Just 



what the limits are is a little bit difficult to say. The pro¬ 
cess is so new that some manufacturers make claims that 
may or may not be proved in practice. It is safe to assume 
that irregularities of .005 in. can be removed with a hone 
and perhaps more. In most cases the cylinder hone is used 
as a final finish after boring or sometimes after grinding. 
Cylinder grinders claim that this is not necessary. Although 
several automobile factories are using the honing process, 
the greatest use of the hone, however, is in the automobile 
repair shop. 

Honing or Lapping Tools will not correct error in axial 
displacement. When this has occurred reboring or regrind¬ 
ing is the only remedy. 


Ill 













THE 


STARRETT 


ROOK 


PISTON FITTING 

Fitting pistons to oversize cylinder bores requires perhaps 
more care and accuracy than any other common operation 
in automobile repair work because, once improperly fitted, 
the error cannot be corrected except by complete refitting. 

Having ground all the cylinders to the new size, the 
pistons are ground to the correct oversize, allowance being 
made for proper clearance. 

When grinding oversize pistons there are many factors to 
be taken into consideration in determining the proper clear¬ 
ance, such as: the material from which the piston is made, 
the make of piston, design and construction of the block and 
the use to which the motor is to be put when the job is com¬ 
plete. The common rule is 
to allow .001 inch clearance 
at the skirt of the piston for 
each inch of piston diameter. 
This varies, however, accord¬ 
ing to the material from 
which the piston is made, its 
design, etc. For example, 
aluminum alloy pistons re¬ 
quire much more clearance 
than cast iron, because alu¬ 
minum alloys expand much 
more than cast iron. On 
aluminum pistons the customary allowance is about .003 to 
.004 in. per inch of bore. On the other hand, constant 
clearance types of pistons, with slit skirts, do not require 
any more—and in some cases, less clearance than cast iron. 
The clearance of the piston tapers from the head to the 
lower edge of the skirt, a 3 inch piston having .003 in. 
clearance at the skirt, requiring .009 in. clearance at the 
head, and .006 in. at a point just below the rings. See 
Fig. 92. - 

Care must be taken also to see that the pistons square up 

112 



Clearance Per 
Inch of Piston 
Diameter 

009 


-.006 


.003 


Fig. 92 —Clearances to Allow 
at Different Points on Piston 
























FOR MOTOR MACHINISTS 


with the connecting rod, a piston aligner being used in this 
operation. 

It should be noted that standard oversize pistons come 
approximately .080 inch oversize—an amount altogether 
too great to remove quickly and efficiently by grinding. The 
better way is to turn the pistons down to within .015 in. of 
the finish size and then complete the operation on a piston 
grinder. In most cases, pistons should be backed off, or 
relieved at the top. 

While, generally speaking, piston clearance for cast iron 
pistons may be taken as .001 in. of clearance at the head of 
every inch of bore diameter, clearances for taxicabs, racing 
cars, trucks and tractors should be from .00125 to .005 in. 
greater and the same generous allowance should be made 
whenever there is reason to believe that the motor is likely 
to be overworked or carelessly driven. 

FITTING PISTON RINGS 

Fitting the rings to new or oversize pistons is every bit 
as important an operation as fitting the pistons themselves, 
or grinding the cylinder bores. No motor can have either 
long life or full efficiency unless the complete piston assembly 
is made with the greatest care and accuracy. 

Piston rings may be divided into three general classifica¬ 
tions—the plain ring, the step-joint, and the “oil-proof” 
ring. There are also the so-called spiral cut rings. The 
difference lies mainly in the kind of joint and types are 
shown in Fig. 93. Each style of ring has its advantages 










THE 


STARRETT 


ROOK 


and disadvantages, and each has a considerable group of 
good repair r^en who prefer it. Whatever ring is used, 
care should be taken to see that it is perfectly round when 
compressed, so that it will bear rightly and evenly at all 
points in the wall of a reground cylinder. 

Piston rings fit into grooves cut in the wall of the piston 
(See Fig. 92) and while it is impractical to try to work to any 
measured clearance, the rings should lie just free in the 
grooves, or so that they can be turned around the piston 
with the fingers. It may be that, when fitting rings to 
new pistons, the grooves are a trifle narrow and in that case 
should be touched up on the lathe, using a fine file which has 
one blind or smooth edge so as not to deepen the groove. 
The proper depth of the ring groove is 1/64 in. greater 
than the thickness of the ring. If the grooves are badly 
worn, however, use an overwidth ring and true up the grooves 
in a lathe or by means of a hand piston regrooving tool. Be 
careful not to try to fit too large an oversize ring in a cylinder 
as it will assume an oval shape under compression, bearing 
on the cylinder wall only at the ring gap and a point diamet¬ 
rically opposite and will leave openings for the gas to blow 
by. Be sure that the ring bears tightly and evenly all 
around the wall of the cylinder and try it for the full length 
of the cylinder to be sure it will not stick when traveling 
with the piston. 

Clearance in piston ring gaps should never be less than 
.005 in., the general practice being to make it .0015 inch per 
inch of cylinder bore with the exception of the top ring which 
should have .003 inch gap clearance per inch of cylinder bore, 
or just twice the amount allowed in the other rings. The 
width of the gap may be readily checked by means of a thick¬ 
ness gage. 

Sometimes new rings are fitted to old pistons and cylinders 
to avoid the cost of a regrinding job. The practice cannot 
be recommended from any standpoint save that of sheer 
necessity, but where followed, rings .005 to .010 oversize 
may be used. 


114 



FOR MOTOR MACHINISTS 


In some cases, oil pumping, or an excessive consumption 
of oil, can be corrected by beveling the lower outside corner • 
of the bottom groove in the piston and drilling 1/16 inch 
holes at an angle, and at equal intervals, through the bevel 
so that the oil will run back into the crankcase. 

FITTING PISTON PINS 

In fitting piston pins great pains should be taken first of 
all to make sure that the connecting rods are neither twisted 
nor bent (See Fig. 94), and that the axis of each cylinder bore 
is exactly at right angles with the axis of the crankshaft as 
was explained under Cylinder Grinding, pages 107 to 110. 

Where no piston aligning jig is available, a* piece of shaft 
the same diameter as the crankshaft may be placed in the 
big end of the rod, the latter held mechanically in a vertical 
position and the squareness of the rod and crankshaft tested 
by means of a square placed on the shaft and on either side 

of the piston. 

The next step in the work, 
after having ascertained 
with an inside micrometer 
—or by other means—the 
oversize pin to use, is to 
ream the bushings in the 
connecting rod or piston 
wall—according to the de¬ 
sign of the motor—in which 
the piston or wrist pin 
turns. 

When reaming a split-end 
rod oversize for an oscillat¬ 



-MANDREL SAME DIAMETER AS CRANK PIN 
Piston Pin 


Fig. 94—Testing Piston Pin 
and Rod Alignment 


ing pin, shim the split, draw the clamp bolt up tight and ream 
until the pin just slips in. When reaming bushed rods allow 
from 0025 to .00075 inch clearance for oil film. A piston 
pin should be so fitted that it will just hold the weight of the 
connecting rod and no more. 

115 




















THE 


STARRETT 


ROOK 


When reaming a piston using the anchored type of pin, 
ream the piston boss opposite the set screw boss so that the 
pin will be a rather tight pressed fit, but be careful that it is 
not fitted so tightly as to run the risk of splitting the light 
metal of the boss. 

With oscillating pins the cast iron piston bosses are the 
bearings and a clearance of from .005 in. for a small pin to 
.001 in. for a large pin should be left. In reaming bronze 
bushed pistons the same clearance should be left as for a 
connecting rod bushing. 

Before fitting aluminum or other alloy pistons with pins, 
the pistons should always be placed in a tub of boiling water 
to heat them to about 200°, at which temperature the pins 
are fitted so they are just free. 

FITTING CRANKSHAFT AND CONNECT¬ 
ING ROD BEARINGS 

Fitting crankshaft and connecting rod bearings is a fairly 
common operation in automobile service stations and repair 
shops and one of great importance and influence on the effi¬ 
ciency of a motor. 

Bearings are commonly fitted in one of two ways. The 
older method is known as “scraping-in” bearings and while 
it is today the common practice in many shops—especially 
where machine equipment is lacking, or the man in charge 
of the work is a thorough machinist and came into automobile 
work from the jobbing machine shop trade—the present ten¬ 
dency is toward “burning-in”. There are perhaps two main 
reasons for this change. “Scraping-in” is entirely a hand 
operation, consuming much time, and it is difficult to charge 
properly for this work in the face of what are called “factory 
flat-rate, time-limit charges” for operations of this sort. In 
order to compete successfully with the “flat-rate” charges 
set by manufactured service stations and factories on this 
work, methods such as the factories themselves followed had 
to be adopted. The other reason is that hand scraping, 
116 



FOR MOTOR MACHINISTS 


technically, does the very opposite of what is desired, for it 
lifts the metal instead of packing it down. 

Whichever method is followed—scraping or burning-in— 
the preparatory work is the same. The crankshaft should 
be tested for alignment, crankpins and main bearings trued 
up and all worn fillets restored. 

A very satisfactory method of restoring fillets is to braze 
on new material with an oxy-acetylene welding torch and 
phosphor bronze filler rod of good grade. The fillets should 
then be machined either on a lathe equipped with offset 
centers (Fig. 96), or on a grinding machine having the 
proper centers for holding this type of work. 

If the crankpins are not too deeply scored, they may be 


Handle 


Fig. 95—Hand Lapping Tools for Crankpins 



trued up wfith a fine file and emery cloth, or better, a hand 
lapping tool such as is shown in Fig 95, and which consists 
roughly of two lead blocks about half as wide as the distance 
between the webs of the crankshaft and turned concave so 
that when brought together, either by clamp screws or 
by pressure on the handles, they will bear firmly and evenly 
on the surface of the crankpin. An abrasive paste of 
fine emery powder and oil is used to coat the lead blocks 
before attaching the tool to the crankpin. When using 
the lapping tool, the proper method is to put the crank¬ 
shaft between centers on a lathe, as in Fig. 96, though where 
a lathe is not available, the crankshaft may be clamped 
to the workbench and the lapping tool turned by hand around 

117 










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the stationary crankshaft. If the crankpins are worn out of 
true to any great extent, they must be turned or ground true, 
and then lapped if a really first class job is desired. Obviously, 
the setup of the crankshaft in the lathe or grinding machine 
will have to be changed as the different crankpins are being 
machined, so that the pin on which the work is being done 




Fig. 96—Methods of Placing Crankshaft Between Lathe Centers 
for Truing Main Bearings 

will revolve on the main center line passing through the 
lathe centers. 

Having trued the crankshaft the next operation is to fit 
the main bearings to the shaft journals. After having 
tested—and if necessary trued up and aligned—the con¬ 
necting rods, the bearing caps should be trued, using a sur¬ 
face plate and Prussian blue, and then dressed down until, 
when clamped on the crankshaft, they grip tightly and require 
shims to make it possible to turn the shaft. The shim thick¬ 
ness required should be about .002 in. and maybe ascertained 
by feeling with a thickness gage under both sides of the cap. 
Care should be taken, and a pair of calipers used to check 
118 






























































































































FOR MOTOR MACHINISTS 


the outside diameters during this operation, that surfaces 
remain parallel so that the bearings do not grip only at one 
end. The connecting rod caps should be treated similarly, 
bringing the work to the point where the bearings themselves 
are to be fitted, either by scraping or burning-in. 

In scraping-in bearings considerable time and handling 
of the crankshaft may be saved by attaching the crankshaft 
to the bench, clamping each 
pair of main bearings together 
with a suitable clamp and doing 
the preliminary scraping on one 
bearing at a time. As soon as 
the ‘ ‘roughing” is accomplished 
the final scraping-in should be 
done with all the bearings in 
place, the crankshaft being in 
position in the inverted upper 
half of the engine base, and 
the crankshaft revolved to de¬ 
termine the area of seating. 

Scraping-in bearings is slow 
and tedious work and requires 
considerable patience and care. 

The entire surfaces of the 
crankpins are smeared, not too 
heavily, with Prussian blue. 

When the bearings are put in 
place, drawn together, and the 
crankshaft revolved a few 
times, the high spots on the bearing are indicated by 
smears of Prussian blue wherever the bearing came in con¬ 
tact with the crankpin. These high spots are removed by 
means of bearing scrapers (Fig. 97) and the bearings again 
tested in the crankpins in the same manner as before. This 
is repeated until the entire inner surface of all the bearings 
seat on the crankpins as indicated by a film of Prussian 

119 



Fig. 97—Bearing Scrapers 























THE 


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blue spread evenly over the inner surfaces of the bearings. 
Before the scraping is started, oil grooves should be cut in 
the bearing with a round-nosed chisel. Do not cut oil 
grooves too deep nor carry them to the extreme edge of 
the bearing. Connecting rod big end bearings are scraped-in 
in the same manner as main bearings. 

In burning-in bearings, the operations are the same up 
to the point where actual scraping begins under the other 
method, the scraping being avoided by placing the crankshaft 
assembly in a burning-in machine. When clamping the 
work in place be sure that the main axis of the crankshaft 
lines up with the axis of the driving spindle on the burning-in 
machine. While burning-in do not revolve the crankshaft 
faster than 100 R. P. M. and use plenty of oil or, as is some 
times recommended, revolve the shaft at about 250 R. P. M. 
using no oil up to the point where the skin of the bearing 
begins to melt and forms clear around the shaft. . At this 
point the machine is stopped, the bearings heavily oiled 



Fig. 98—Burning-in Machine 

120 




































FOR MOTOR MACHINISTS 


and the bearings run in under power until they become well 
burnished. 

When the bearings become heated they should be allowed 
to cool and then removed and inspected for bearing surface. 
When the bearing surface is less than 90% of the total sur¬ 
face of the bearing a thin shim should be removed, or the 
cap dressed down, and the bearing again burned-in. On 
crankshafts with forced feed lubrication—or shimless main 
bearings—there should be a little looseness (.002 in. approx.) 
between the cap and the seat to permit an oil film to form 
between the pin and its bearing while burning-in. 

VALVE FITTING 

Valves of cars which have seen much service should be 
very carefully examined before any attempt is made to refit 
them, as often it is cheaper and better to replace the old 
valves with new ones. Both valves—including the valve 
stems—and valve stem guides should be carefully examined 
for wear. Any valve stem that is worn or which has as 
much as .008 in. clearance in the guides indicates a need for 
a new valve, a new guide, or both. On every valve stem 
there is a small section which never enters the guide and is 
therefore never worn. Before grinding an old valve, it should 
be tested between centers to see if it runs true on the worn 
section of the stem. If it runs true, the valve may be ground 
either between centers or while held in a collet chuck which 
grips the unworn section of the stem. When the valve does 
not run true on the worn section, it should be ground while 
held in a collet chuck which grips the worn section at a point 
that will average up the wear, so that the valve heads will 
more nearly fit the seats when the worn stems are replaced 
in the worn guides. In most cases, however, a valve whose 
stem is worn badly enough to require this latter method of 
grinding should be replaced. In examining the heads and 
stems, a micrometer should invariably be used. 

Warped or bent stems are seldom, if ever, worth straight- 

121 



THE 


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ening, because in most cases the valve stem guide has been 
worn out of true. However, when no new valve is available, 
the old stem may be straightened by placing the valve be¬ 
tween lathe centers and crowding the stem over with a tool 
rest until it runs true. They should, however, be exchanged 
for new valves at the first opportunity, for a properly fitted 
valve has but .0025 to .003 in. clearance in the guides and 
it is almost impossible to straighten bent stems so that they 
won’t bind. 

Valve faces and seats, improperly ground or pitted, should 
be refaced before grinding in, as should also be done in cases 
where the valve head is warped. In refacing valve seats a 
reseating cutter should be used, the edges of which are at 
the proper angle for the motor on which the work is done. 
The stem of the reseating tool should be the same size as the 
valve stem in order to keep the tool as rigid as possible. In 
refacing a valve seat take off no more metal than is absolutely 
necessary. Valve seats that are too wide may be reduced 
by counterboring the valve chamber, leaving a seat from 
1/16 to 3/32 in. wide. Counter boring is preferable to boring 
because the latter method often prevents the use of standard 
diameter valves. For refacing the valve it should be placed 
in a regular valve grinding machine or—if that is not avail¬ 
able—the stem end should be held in a universal chuck on 
the shop lathe, with the tailstock center of the lathe in the 
countersink on the head of the valve. The job may then 
be done with a tool-post grinder set at the proper angle, the 
valve rotating at low speed, and the grinder moved back 
and forth by the compound rest feed screw. Again, be care¬ 
ful to remove no more metal than is absolutely necessary. 

The valve stem guides should now be examined and if new 
valves with oversize stems are being put in, should be either 
reamed or replaced. New valve stems should be lapped into 
the guides in the same manner as a new piston is fitted. 
When the weight of the valve will cause it to move very 
slowly to the bottom without stopping until the valve head 

122 



for motor m achinists 


rests on the upper end of the guide, it may be assumed that 
the fit is correct. In reaming valve guides, care must be 
taken to keep the reamer central. Use a very light pressure 
so that the reamer will cut its new path rather than follow 
the old hole. 

The next step in operations is the grinding-in of the valve 
on the valve seat. In some of the smaller shops, not equipped 
with proper valve grinding machines, “grinding the valve” 
and “grinding-in on the valve seat” are synonymous. The 
better way, however, is to “grind the valve” on a machine 
designed especially for that work and to view the “grinding- 
in on the seat” more as a lapping operation 
and one that is often unnecessary if the valve 
has been properly ground on the machine and 
the seat reamed with a valve-reseating tool or 
reamer that was ground on the same grinding 
machine and to the same angle as the valve. 

However, when the “grinding” is of necessity a 
hand operation, a coil spring should be placed 
over the stem and under the head of the 
valve (Fig. 99), so that the valve head is about 
an inch above the seat, which is well coated 
with grinding compound, and the valve turned 
in the seat by means of either a hand or electric 
valve grinding tool. After every few turns the 
tool should be lifted enough to shift the position of the valve. 
After rough grinding the operation is repeated, using a very 
fine grinding compound until the entire surface of the valve 
face is silvery in appearance. Both valve and seat should 
then be thoroughly cleansed of all traces of the grinding 
compound and the valve permanently inserted. Some 
machinists finish the job by lapping the valves in with 
kerosene, which gives a high polish to the seats and tends 
to prevent carbon deposit. The seating of a valve may be 
tested by coating the seat with Prussian blue just as is done 
in fitting main and connecting rod bearings. While grind¬ 
ing the valves the valve ports should be stuffed with waste 

123 







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or rags to keep the grinding compound from getting into the 
valve guides or cylinders. 

It is generally considered good practice to decarbonize the 
motor—either by scraping or burning-out—whenever the 
valves are ground, because once the carbon crust is disturbed, 
it will continue to flake off and will work under the valves. 

Valve tappets should be adjusted when the engine is 
warm, using a thickness gage and allowing from .002 to .005 
inch clearance, according to standards recommended by the 
various manufacturers. Valve clearances should be adjusted 
while each cylinder is on its compression center. If the valve 
adjusting screws have had hollows pounded into their ends 
they should be ground flat. This may be done by placing 
them in the chuck of a drill press and running them against 
an oil stone lying on the drill press table, or by grinding them 
in a proper grinding machine, such as was used to grind the 
vdves. 

LAPPING BEARINGS 

As has already been noted, bearings often have their fitting 
completed by lapping. This consists in putting a special 
bearing lapping compound in the bearing and lapping it to 
the shaft. This works very well with bronze bearings, but 
care must be taken to see that the right kind of compound is 
used with babbitt because there is likelihood of the compound 
imbedding in the soft babbitt and thereafter gradually 
grinding the steel shaft down. A compound that breaks 
down and disappears or dissolves is necessary for use with 
babbitt. 

ANTI-FRICTION BEARINGS 

Ball and roller bearings need no fitting. The inner and 
outer races are finished to close limits and replacements are 
made by driving out the old parts and driving in the new 
parts. Care must be used to drive straight so as not to 
cock the race. Roller bearings of the flexible roller type 
have an outer shell which is split and therefore requires little 

124 



FOR MOTOR MACHINISTS 


pressure to remove or replace. The rollers usually operate 
directly between this shell and the shaft. Adjustment is 
possible in some types of anti-friction bearings and in some 
other types there is no adjustment. 

FITS AND FITTING* 

Various kinds of fits are used in automobile construction. 
In some cases the fit is fairly loose, or has clearance so that 
the parts are free to move on each other. In other cases the 
fits are made very tight and are called driving fits. 

Running Fits 

Parts that are to move on each other at varying speeds 
are given sufficient clearance—known as a running fit—to 
enable them to perform their duties with a minimum of 
friction. The kind of metal and degree of heat attained by 
the part under running conditions determine the amount of 
clearance. Some examples of running fits are the main and 
connecting rod bearings, camshaft bearings, pistons, cooling 
fan, rear axle and propeller shafts (the running fits being in 
the ball, roller or bronze bearings), and the front and rear 
wheel bearings. 

Driving Fits 

Some parts require a driving fit against another part. 
Practically all the solid bronze bushings such as used in the 
steering spindles, piston pins, reverse shaft and propeller 
shaft front bearings are driven or forced into machined open¬ 
ings. The outer races of ball and roller bearings are a driving 
fit in the wheels, castings or wherever they go and the inner 
races are a driving fit on the shafts. The balls or rollers are 
a running or really rolling fit between the two races. 

Shrink Fits 

There are a few places on the automobile where a shrink 
fit is used. In some cars the flywheel starter gears are made 

* See also pp. 29-33, Vol. I, Starrett Books, and pp. 14-18 and 152-154, Vol. II, 
Starrett Books. 

125 



THE 


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as separate rings which are heated to expand them, slipped 
over the flywheel and cooled. As the fit is made very close 
in machining, the ring shrinks on the flywheel when it cools 
and is immovably fixed if the work has been properly done. 
Damaged flywheel gears are quite often replaced by turning 
off the old gears and shrinking a new gear on. 

Taper Fits 

Several parts of the automobile are fitted with a taper, 
key and nut. The inner and outer tapers are accurately 
machined and the key is usually of the Woodruff or half¬ 
moon type. By tightening the nut on the shaft the part is 
driven fast on the tapered shaft and also prevented from 
turning by the key. The pinion gear is fastened to the 
rear of the propeller shaft or pinion shaft in this way and the 
rear wheels are fastened to the axle shafts in the semi-float¬ 
ing type of axle in the same manner. 

BENCH WORK* 

Bench work includes laying out, chipping, filing, polishing, 
hand reaming, hand tapping, and all the many shop jobs 
done at the bench or in a vise. 

LAYING OUT 

This is the shop term which includes the placing of lines, 
circles, and centers upon curved or flat surfaces for the 
guidance of the workman. It is somewhat analogous to 
mechanical drawing. It differs in one important respect, 
however, that while a line drawing is seldom scaled and 
therefore exact accuracy of spacing is not required, in laid- 
out work, the lines, circles, centers, etc., are to be followed 
exactly. All lines, centers, etc., should, therefore, be exactly 
located and placed, and all scriber, divider, and center points 
should, while in use, be exact and sharp. Particular care 
must be maintained to insure fine and accurate laying out. 

* See also pp. 35-42, Vol. I, Starrett Books. Also pp. 52-60, Vol. II, Starrett 
Books. 

126 



FOR MOTOR MACHINISTS 


Preparing the Surface 

If no work of special accuracy is desired, carefully rubbing 
chalk, or white lead mixed with turpentine, upon the surface 
of the work will be sufficient as a coating. For fine exact 
layouts a special marking solution must be used. The one 
in common shop use is a mixture of one ounce copper sul¬ 
phate—or blue vitriol—to four ounces water. A little nitric 
acid may with advantage be added. This solution applied 
to a cleaned iron or steel surface gives a dull coppered surface, 
and the finest line scribed upon it is brilliantly visible.. 
Still another method used on die, or other extremely fine 
work, is to heat the piece to a blue before scribing. 

Scribing Lines 

The usual scribing points are those common to dividers, 
hermaphrodite calipers, scratch awls, scratch gages, surface 
gages, and trammel points. Combined with the. scribing 
points may be used steel rules, bevel protractors, steel 
squares, steel straight edges, levels and measuring rods, 
micrometer or vernier height and depth gages, and the 
various center punches. Ability to so combine and make 
use of the various tools as to insure accuracy is a considerable 
asset to the man who does laying out. 

Protractors 

As made for machine-shop use the common protractor is 
provided with attached straight edges, and can be used either 
to measure or to lay off lines at an angle to each other. 
Measuring the angularity of two or more lines with a pro¬ 
tractor is termed “reading the angles”. As oftentimes its 
use is determining the angle made by two surfaces (a bevel), 
the tool is usually termed a bevel protractor. Protractors 
for common shop use are graduated to degrees through a 
length of circumference of one hundred and eighty degrees. 
An attached vernier enables the user to read angles to one- 
twelfth of a degree (five minutes). 

127 



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Laying-Out Plate 

If desirable results are to be obtained in laying out flat 
work, special metal plates upon which to rest the work and 
the tools must be provided. These are known as leveling, 
surface, or laying-out plates; they furnish an accurate plane 
surface upon which work and tools may be placed. The 



Universal Bevel Protractor with Vernier and Acute 
Angle Attachment 


size of these plates varies from those of small areas used in 
laying out small jigs, etc., to those for large pieces, having 
sides several feet in length. The work may be laid directly 
upon the surface of the plate or held upon leveling strips, 
blocks, or parallels placed on the plate. In other cases it is 
convenient to clamp the work to knee or angle irons, which 
are then placed upon the leveling plate. 

128 

















FOR MOTOR MACHINISTS 


CHIPPING 

Formerly many of the surfaces of machine parts were 
hand-chipped and filed to a fit. While the mechanic in the 
modern shop can usually find methods of machining most 
of the surfaces he needs to fit up, there are still occasions 
when the work has to be hand-chipped. 

Tools Used 

The common chipping tools are a hand hammer and a 
cold chisel. The hand hammer should weigh not less than 


Fig. 100—Chipping 

129 















































THE 


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three-quarters of a pound nor over two pounds, and may be 
either of the ball pein or flat pein type. A chipping ham¬ 
mer should balance well in the hand when fitted to a handle 
not more than sixteen inches long. The handle near where 
it enters the hammer should be thinned and worked down to 
a shank that is somewhat flexible, so that the shock to the 
arm and hand will be less. The face of a good chipping 
hammer should crown slightly. 

Chipping chisels, ordinarily termed cold chisels, are of 
various sorts, and are often known by the shape of the cut¬ 
ting end; for example, flat, cape, roundnose, diamond, and 
gouge chisel. The steel from which they are made should 
be eighty to ninety point carbon, of octagon cross-section, 
with the cutting end forged to the desired shape, well packed 
by the forge hammer, hardened, and the temper drawn 
to a blue. The hammer end of the chisel should be forged 
from the octagon to a reduced round, but not hardened. 
Flat-chipping and cape chisels should be ground with 
straight, symmetrical cutting edges, at as acute an angle as 
the nature of the work will permit. 

In hand-chipping the hammer handle should be grasped 
near the end and the hammer swung free from over the 
shoulder with an easy forearm movement. Hold the chisel 
loosely in the hand at an angle with the work that permits 
an even chip of right depth. The vision should be directed 
to the cutting edge of the chisel, rather than at the end struck 
by the hammer. Avoid gripping hammer or chisel tightly, 
as this rapidly tires the hand and arm. 

In shops which have compressed air, use is made of the 
modern pneumatic chipping hammer, which does remarkable 
work of the heavier sorts. 

Cold chisels are ground on an emery or other type grind¬ 
ing wheel. Care must be used not to burn the steel by over¬ 
heating it on the wheel. A pot of water should be kept 
near the wheel and the point of the chisel dipped in the 
water every few seconds to keep it cool. If the bright, ground 

130 



FOR MOTOR MACHINISTS 


edge of the tool should turn blue from the heat any time, that 
part has been overheated and will have lost its temper. Such 
an edge will turn over as soon as it is used on work because 
it will be too soft. 

It is necessary in such a case to reharden and re temper the 
tool. In hardening and also in forging, the chisel should be 
heated to a cherry red. If the chisel is forged when it is 
below a cherry red, the steel will most likely split or check, 
and when used later, little chips will break out. If heated 
beyond a bright cherry red, the steel will burn, throw off 
bright sparks and become pitted. 

For chipping very heavy iron or steel castings, the angle 
of the cutting edge can be as blunt as 90 degrees or a right 
angle. For lighter work, brass, bronze, etc., the angle can be 
sharper, say about 60 degrees. 

In automobile work, chisels often require a special grind¬ 
ing. For instance, in cutting the rivets from worn out brake 
linings and clutch facings, it is very much better to grind all 
on one side, the other side being flat like a wood chisel. For 
cutting oil and grease channels in bronze and babbitt bear¬ 
ings and bushings, the chisel is more the shape of a punch 
with a round sharp edge. A heavy chisel with a very blunt 
edge is used for cutting off bolts on wheel flanges and for 
cutting off rivet heads. 

WELDING, ETC. 

Metals may be joined together or be separated by means of 
heat. Joining processes of this kind are known as welding, 
brazing, soldering and lead burning. Welding produces the 
strongest joint. It may be done with an oxy-acetylene flame 
or by means of an electric arc, either of which are capable of 
melting any of the metals used in automobile construction. 
Welding is used for cast and wrought iron, steel and aluminum. 
In any case, the adjoining surfaces to be welded together are 
brought to the melting point and additional metal is 
melted from a rod of the same material and flowed over in 
131 



THE 


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sufficient quantity to fill up the gap. In welding certain 
kinds of articles like cylinder castings, gear wheels, etc., pre¬ 
heating with a gas flame is necessary so that there will not 
be strains set up in the piece due to unequal contraction. 

Aluminum welding does not require such a high degree of 
heat, but the metal oxidizes very rapidly and it is necessary 
to use welding flux to prevent this oxidation. 

The possibilities of welding are almost unlimited. The 
process can be used for patching, building up worn parts, 
repairing cracks, etc. The welding flame can also be used 
for cutting shafts, frames, etc. Solid rubber tires and rims 
that are of no further use can be cut off the wheels with the 
torch. The odor is objectionable, but the operation is some¬ 
what quicker than other methods. 

Brazing 

This is sometimes known as hard soldering and consists of 
joining iron or steel parts with a softer metal such as brass 
or bronze. A gas flame is employed, this not being sufficient 
to melt the iron or steel, but to bring it to a dull red heat. A 
flux such as borax is used to prevent oxidation and the brass 
solder or spelter applied and melted as desired. Brazing is 
often employed to repair cracks in cylinder water jackets 
where great strength is not required. Brazing is also used 
in connection with riveting to make a stronger joint than 
the rivets alone would afford. 


Soldering 

Soldering is done with a solder composed of various parts 
of tin and lead. A good solder, called half-and-half, consists 
of equal parts of tin and lead. Radiator repairing is done 
by soldering, the parts of the radiator being made of brass 
and copper which take solder very well. It is necessary 
that the surfaces to be soldered, as well as the soldering iron 
itself, be mechanically and chemically clean, The work is, 
132 



FOR MOTOR MACHINISTS 


therefore, scraped and then covered with a soldering paste 
of some kind. There are many such preparations that are 
far superior to the old, time-killed muriatic acid. There 
are also self-fluxing solders which are effective and quick to 
work with. There is an increasing tendency to solder elec¬ 
trical connections and joints to prevent corrosion and pos¬ 
sible breakage. 

Lead Burning 

Storage batteries have their cells connected by means of 
lead posts and straps. When overhauling batteries it is 
necessary to break these connections and in reassembling 
the connections must be again joined. This is done by lead 
burning, which might be best described as lead welding, as 
the parts are brought to the melting point and more lead 
melted in to fill up the space. Certain molds for the posts 
and straps are necessary in carrying out the work. Besides 
the gas or oxy-acetylene flame, the electric arc is also em¬ 
ployed in this work. The lead used is pure lead with some¬ 
times a slight amount of antimony added to secure hardness. 

DECARBONIZING 

Oxygen by itself is used for decarbonizing cylinders. The 
oxygen is introduced through the spark plug holes by means 
of a copper tube and the carbon ignited with the flame from 
a match, the carbon burning completely away in the atmos¬ 
phere of oxygen. The process is particularly favored on 
engines of the solid head type where the removal of carbon 
by scraping—although it is commonly recognized as better 
practice—would necessitate the removal of the cylinder block 
and the taking out of the pistons. If the pistons are kept 
at top position during the burning and means taken to pre¬ 
vent fires from the sparks, this method of carbon removal 
can do no damage to the car or its parts. The gasoline sup¬ 
ply must be shut off and the carburetor and fuel lines drained 
before starting to burn out the carbon. 

133 



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THE ACETYLENE TORCH 

The acetylene torch has found a great deal of use in the 
automobile repair shop. Its principal function is in welding 
broken metal parts, but it is also very useful for heating 
parts to be bent and in removing the carbon from cylinders. 

The apparatus required consists of a tank of oxygen and a 
tank of dissolved acetylene, a torch with a number of dif¬ 
ferent size tips, gages for the tanks, a reducing valve and a 
decarbonizing tip for carbon removal. The equipment is all 
purchased outright with the exception of the gas tanks which 
are returned for refilled ones from time to time. 

Welding of all kinds can be performed with the acetylene 
torch. Metals such as cast iron, steel forgings and alumi¬ 
num can be welded and brazing or hard soldering can also be 
done. Where the parts to be welded are small, they are 
prepared by cutting a channel for the weld or otherwise 
preparing the edges after which the torch is played on the 
edges in a systematic motion until they are about to melt. 
The welding rod, which is of the same metal as the parts to 
be welded, is then melted in the flame and the-parts all melt 
or weld together. A suitable flux is used to prevent oxida¬ 
tion. In welding aluminum, special care has to be taken as 
the metal oxidizes very rapidly, and unless the weld is free 
of the oxide, the strength will be reduced or the metal will 
not weld at all. 

Large work such as cylinder blocks have to be preheated 
in a preheating furnace because otherwise the expansion and 
contraction caused by the excessive heat at one point would 
result in the weld cracking as soon as it cooled. 

When cars come into the shop with bent axles and frames, 
the heat of the welding torch is very helpful in bending them 
into alignment again. Front axles are made with a very 
high factor of safety, therefore it does not do any great deal 
of harm to soften them in the flame. Small parts such as 
steering knuckles should never be heated to bend them as 
the heat treatment will be destroyed and the part will be so 

134 



FOR MOTOR MACHINISTS 


weakened that it will be a source of danger. Neither should 
these small parts be bent cold as there is liable to be a fracture 
in the metal. The best thing to do is to replace the damaged 
parts with new ones. 

In removing carbon from the cylinders, the gasoline is first 
drained from the carburetor to prevent any possibility of fire. 



Fig. 101 — Gap Lathe with Equipment for Automobile Repair 
Work 


The spark plugs are removed and the crank turned till the 
pistons are at top dead center. The decarbonizing tip is 
then attached to the oxygen tank. No acetylene is used, 
only oxygen. The tip of the tube is inserted through the 
spark plug hole and a lighted match dropped in after turning 
on the oxygen. The carbon will then burn in the atmosphere 
of oxygen until it is all consumed. If any remains, a scraper 
is used to stir it up a little, after which the process is repeated. 

THE LATHE* 

The engine lathe is capable of producing the largest variety 
of products of any of the machine tool family and—because 
of its versatility and the almost infinite number of operations 

* See also pp. 65-96, Vol. I, Starrett Books, and pp. 27-28, 107-112, 134-141, 
150-151 and 156-157, Vol. II, Starrett Books. 

135 













THE 


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ordinarily performed on special machines, but which can be 
done on a properly equipped lathe—should be part of the 
tool equipment of every garage or repair shop that makes 
any pretense to render complete service or which intends to 
operate at a profit. 

For repair shop work a gap lathe, such as is shown in Fig. 
101, is recommended. The gap in the bed makes it possible 
to swing much larger work—such as flywheels, etc.—than 
would be possible in lathes with solid beds and it will accom¬ 
plish everything that the ordinary lathe will do. The lathe 
should have quick change gear box, screw-cutting attach¬ 
ments, elevating compound rests, hollow spindles, chucks, 
face plates, dogs, steady and back rests, etc., and automatic 
longitudinal and cross feeds. It should be capable of cutting 
any number of threads per inch from four to forty. 

Care of the Lathe 

Lathes, like all other machine tools, require care. Especial 
attention should be given to applying a suitable machine oil 
to all the bearings, for improper lubrication of the wearing 
surfaces is one of the immediate causes of excessive wear. A 
medium-size, flexible-bottom oil can is best for this pur¬ 
pose, and oiling should be frequent on those bearings which 
are given the severest service, either from excessive pressure 
or from high speed rubbing. All oil holes should be kept 
free and clean, and where possible should be protected from 
dirt. Those bearings, as, for example, the ways upon which 
the carriage moves, which by construction are hard to protect 
from dirt, should be frequently cleaned and re-oiled. At least 
once a week the lathe should receive a thorough cleaning, and 
it is recommended that the bearings be washed out with 
kerosene, as a plugged oil hole prevents the proper lubrication 
of the bearing. Never lay files, etc., on the ways of a lathe. 

Indicating and Adjusting 

Upon the condition of the centers rests to a large degree 
the accuracy of the work produced by the lathe. After 
136 



FOR MOTOR MACHINISTS 


lubrication of the lathe, the centers and the tapered holes in 
which they fit, should be cleaned and tested. The “dead” or 
tailstock center should have a hardened point to resist wear. 




The cone-points of the centers should be smooth and an 
exact 60°. These centers should align with each other in 
the vertical and horizontal planes, and the “live” or head- 
stock corie-point should rotate truly concentric with its axis. 

The trial and error method of adjusting the centers in 

137 




























THE 


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alignment is to first bring the cone-points nearly into con¬ 
tact, and by adjusting the tailstock frame upon its cricket 
bring them into as exact truth as is reasonably possible. 
With the footstock clamped in position to receive the work, 
surface the diameter of a trial piece for a length sufficient to 
allow testing its diameter at several places. If the diameter 
increases or decreases as the tool passes along the length of 
the work, readjust the tailstock and repeat the test until the 
required degree of accuracy is obtained. To test the live 
center for concentricity, place in the tool-post a universal 
test indicator, as shown in Fig. 102, with the feeler in touch 
with the cone-point. Rotate the headstock spindle slowly 
by hand and note the dial. If the dial shows an eccentricity 
in excess of the allowed limits for the job to be done, the cone- 
point should be machined true. In cases where it is custom¬ 
ary to have the live as well as the dead center hardened, the 
cone-point must be trued by some grinding attachment, as, 
for example, a tool-post grinding fixture. By many workmen 
the live center is left unhardened and can be trued with a 
square nose cutting tool and the compound rest—if such is a 
part of the lathe’s construction—and afterward lightly filed 
to a smooth surface. To test either center for its cone-point 
angle, use is made of a center gage, shown in Fig. 103. 

A common practice to facilitate correct positioning of the 
live center, which often has to be removed, is to mark in some 
way both the center and collet, or spindle holding it, so when 
putting the center back in the spindle the two marks will be 
in alignment or opposite. This insures a truer center and 
whenever necessary to grind or turn true the marks should 
be opposite. 

Another common practice, which should be borne in mind 
and may be well to mention here, is when removing the live 
center to do work in the chuck, which screws onto the spindle, 
a piece of waste or even cloth or paper should be stuffed in 
the hole in the spindle to prevent the collection of oil and 
chips. If this is neglected, the chips will become imbedded 

138 



FOR MOTOR MACHINISTS 


and prevent the center and collets from running true. 
Briefly, oil and dirt should never be allowed to gather at 
either of the centers’ bearings. 

TEST INDICATOR 


This is a tool for indicating minute contact variations upon 
a graduated dial or upon a graduated arc. The graduations 
are usually one hundred in a complete circle with an easily 
read width of spacing. The instrument is built in such a way 
that one of these spaces represents a movement of the con tact- 
point of 1/1000 inch. Skill and experience on the part of the 
workman will permit variation of as little as .0005 inch to be 
read with ease and accuracy. However, if the work is true, 
there will be no variation or movement of the needle-point. 

Various mechanisms are employed for multiplying the 
movement of the contact-point, all of which are based upon 
a combination of short and long arm levers. 

The test indicator may be used with advantage in any of 
the common machine tools to indicate eccentricity in the 
lathe, milling machine, or grinding machine; to indicate 
uniformity of height in the 
planer, shaper, boring ma¬ 
chine, or milling machine; 



to indicate parallelism, 
and to test for alignment 
in any machine. 

Fig. 104 —Test Indicator 

139 






THE 


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Fig. 105—Truing Work in Chuck 



Fig. 106—Truing Jig on Face Plate 



Fig, 107—Indicator Used with Surface Gage on Bench Plate 

140 




































FOR MOTOR MACHINISTS 


WORK CENTERS 

Most turned work is done upon the lathe centers, and it is 
necessary to provide suitable cavities in the work, coned to 
fit the cone-points of the lathe centers. This is termed 
“centering the work”, and consists in first locating the posi¬ 
tion of the cavities and afterward drilling and reaming them 
to form and size. The usual practice is to use a combination 
drill and countersink, as it insures exact concentricity in the 
hole, as well as being a quick method of doing the work. 


LOCATING THE CENTERS 

It is evident that the centers should be so located that the 
entire diameter of the turned job 
shall finish to size. Beside this, 
efficient turning demands that 
the chip taken shall be’ of prac¬ 
tically uniform depth as the work 
rotates against the cutting tool. 
For these reasons accuracy in 
centering is necessary. Where 
the turned job is made from 
ordinary bar stock, the centers 
may be located by scribing lines 
at an angle across the ends, using 
a combination square blade with 
a center head and the scriber pro¬ 
vided. In place of this tool, a 
hermaphrodite caliper may be 
used to scribe the ends of the 
stock. The center is located with 
a center-punch at the intersec¬ 
tion of the scribed lines and the 
concentricity tested by spinning 
the bar upon the lathe centers. If 
necessary, the center-punch marks 
are shifted. If the piece is bent 

141 



Fig. 108 —Hermaphrodite 
Calipers 




THE 


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it must, after centering, be straightened to reasonable truth. 

The work should never be straightened in the lathe centers 
unless it is extremely light. Any strain of bending will 
throw the lathe centers out of line as well as imposing strains 
on the lathe parts that they are not intended to receive. 



Fig. 109 —Typical Lathe Tools 


When the job is to be turned from a forging, it is usual to 
roll the forging on straight edges and scribe lines across the 
ends, using a surface or height gage. In such cases the forg¬ 
ing is so located with reference to the straight edges as to give 
a fair average of the surface errors due to forging. It is also 
usual to leave a greater excess of stock for finishing purposes 
upon a forging than upon rolled bar stock. When the centers 

142 





FOR MOTOR MACHINISTS 


are well located the holes may be drilled under a drill press 
or in a hand lathe, as convenient. Where much bar stock 
must be centered a special self-locating centering machine 
is often used. 

LATHE TOOLS 

A typical set of tools for use in the engine lathe is shown 
in Fig. 109, and their uses indicated in Fig. 110A. While 
in common shop language all these are known as cutting 
tools, technically speaking, many of them separate the stock 
in a manner that is analogous to crowding off the metal 
rather than by a strictly cutting action. Cutting in its 
proper sense is a splitting action, and a properly ground 
and properly set cutting tool is a wedge in that it splits off 
the excess stock. Among the common lathe tools, the side 
tool (Nos. 1 and 2, Fig. 109), and the diamond-point tool 
(Nos. 4 and 5, Fig. 109), are the best examples of wedge or 
splitting action. 

The nose of a cutting tool has several sides, two of which 
come together at some angle to form a cutting edge. The 
angle formed by these surfaces must be sufficient for strength, 
and must contain enough metal to conduct away the heat 
generated by the cutting action. For turning ordinary soft 
steel and soft gray iron an angle of sixty degrees is good 
practice. For harder materials the angle may be increased. 
In the case of forged lathe tools, the working end of the tool 
is forged upon the end of a short piece of square or rectangular 
bar stock. The length and size of the shank of the forged 
tool depend upon the size of chip and the machine used. 

Rake 

The angle which the upper side of the tool makes with the 
horizontal is termed the rake. If the slant is away from the 
work it is termed front rake; if in the direction of the axis of 
the work, it is termed side rake. A cutting tool may have 
its upper face forged and ground with either a front or a side 
rake or a combination of both. (See Fig. 110.) 

143 



THE 


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Clearance 


By clearance is meant the angle which the underside of the 
tool makes with the vertical. (See Fig. 110.) As in the 
case of “rake”, the clearance directly away from the axis of 
the work or lathe is termed front clearance, while that along 
the axis of the work is known as side clearance. With the 

_tool in cutting position the 

i\,—<[0 > clearances must be in any 



case not less than three degrees, and in most cases not 
more than ten degrees. Experience is the best teacher. 


Right-Hand Tools 

These are tools having the rake, clearance, and cutting 
edges formed to turn or square from the right toward the 
left. 

Left-Hand Tools 


When the rake, clearances, and cutting edges are formed 
to cut from the left to the right the tool is known as a left- 
hand tool. 

USES OF LATHE TOOLS 

The common uses of standard lathe tools are shown in 
Fig. 110A. The arrow in the diagram indicates the direc- 
144 

















FOR MOTOR MACHINISTS 


tion of tool feed, the work turning toward the tool in all 
cases. 

Left and right hand side tools, Nos. 1 and 2, Fig 110A, 
are shown in use for facing the side and end of a collar and 
shaft respectively. Either tool can be fed in or out and can be 

worked into a shoulder. In 
some cases a bent or offset 
side tool, such as No. 3, 
Fig. 110A, is preferable as 
it will reach work sur¬ 
rounded by a flange or col¬ 
lar, as for instance a boss 
or lug on the inside of a 
brake drum, or wherever a 
cross-rest would interfere. 

For straight turning, the 
diamond point tools, Nos. 
4 and 5, Fig. 110A, are 
used. The only difference 
in these two tools is that 
the rake and clearance are 
ground on opposite sides so 
that one tool cuts while 
Fig. 110A—Uses of Lathe Tools feeding to the left, while the 

other cuts when fed to the 
right. A round-nose tool, No. 6, Fig. 110A, is very often 
used for straight turning operations and, like the diamond 
point tools, may be ground to form either a right or left hand 
tool. 

No. 7, Fig. 110A, is a cutting-off or parting tool and is 
used for necking down or cutting off stock. In motor work 
it is often used for relieving shoulders and corners previous 
to grinding operations. 

Three'forms of right-hand threading tools are shown in 
Nos. 8, 9 and 12. Fig. 110A, Nos. 8 and 9, are cutting external 
and No. 12, internal thread. No. 8 is used for work where 
the thread does not run up to a shoulder, No. 9 being used 
145 


if II II 



It 

10 u 












THE 


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in the latter case. No. 10 is used for rough turning opera¬ 
tions and is similar to No. 6, except that it has a longer 
cutting edge, enabling it to be fed in for a deeper cut. 

No. 11 is a boring tool and is ordinarily ground with a 
round nose except when it is necessary to work into a square 

shoulder. For such work 
the boring tool may be 
ground with a diamond 
point. Boring tools are 
often built up from a com¬ 
bination of a tool-holder 
carrying a cutter bar with 
the cutting bit inserted as 
shown in Fig. 110B. A 
similar type of cutter is 
commonly used for inside thread cutting, except for very 
small holes. 

The upper section of the bar shows it fitted with a cutter 
for straight boring, which 
may be replaced with a 
thread cutting tool. The 
lower section shows the 
type of cutter used for 
working close to a shoulder. 

Fig. 110C shows, mounted 
in a special tool-holder, a 
type of boring tool used Fig. HOC— Boring Tool and 

for boring very small holes. Holder for Small Diameter Holes 


Fig. 110B—Boring Tools with 
Inserted Cutters 


SETTING LATHE TOOLS 

It is very important that the lathe tool be properly set 
in relation to the axis of the work and the direction of the 
cut. While there are exceptions, notably that of the Siamond 
point, lathe tools are usually set with the cutting point at 
the exact height of the axis of the lathe. (See Fig. HOD). 
In the case of the diamond point, the front clearance is 
146 










FOR MOTOR M A C H I N I S T S 


usually forged to fif¬ 
teen degrees or over. 
It is necessary, there¬ 
fore, to set the point 
above the axis height 
to obtain a working 
clearance of not to ex¬ 
ceed ten degrees. Five 
degrees is usually con¬ 
sidered correct. (See 
Fig. 110E.) Unless 
the cutting tool has a 
bent shank it is usu¬ 
ally set at right angles 
to the surface of the 
work. 

GRINDING LATHE TOOLS 

Lathe tools made from carbon tool steel should be sharp¬ 
ened by grinding upon a wet emery-grinder, or upon an 
ordinary water-drip grindstone. If made from the newer 
high speed steels, the grinding should be upon a dry and 
rather coarse abrasive wheel. The grinder should have a 
suitable work-rest upon which to support the tool in sharp¬ 
ening the larger tools, or for resting the hands in the 
case of the smaller tools. 

For purposes of safety, 
the work-rest should be 
firmly and securely 
clamped as close as pos¬ 
sible to the used face of 
the wheel. The grinding 
may be done upon the 
periphery of a disk-wheel 
or upon the sides of a 
cup-wheel, as desired. In 



Fig. 110E—Correct Position 
of Diamond Point Turning 
Tool When Cutting 



Fig. HOD —Thread Cutting Tool Set 
at Height of Lathe Center 


147 











THE 


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any case the wheel should rotate to force the tool upon the 
rest rather than from it, and should run true and in balance. 
Efficient cutting depends very largely upon the correct sharp¬ 
ening, as well as the correct setting of the cutting tool, and 
great care should be taken when grinding a lathe tool to 
have the several faces true and making correct angles with 



each other. The manner in which this is done is a pretty 
good index of the workman’s skill. It is good practice to 
dress the cutting edge of a lathe tool by hand, using a small 
oil stone, after the tool is ground. 

TESTING CUTTING ANGLES 

The usual lathe-cutting tools have well-defined cutting 
edges, and the angularity of the surfaces which meet to form 
the cutting edge can be measured with a bevel protractor, 
or, in the case of a sixty-degree angle, the center gage may 
be used. The center gage is also used to test the angle when 
grinding a vee-pointed thread tool, as illustrated in Fig. 111. 
148 





FOR MOTOR MACHINISTS 


TOOL HOLDERS 

The high cost of the materials used for modern cutting 
tools has resulted in the marketing of a variety of holders 
designed to hold cutting points and by their use a large 
number of relatively inexpensive cutting points are made to 


Fig. 112—Tool Holder 



interchange in a single shank or holder. One form of tool 
holder is made to hold all points forged in the regular forms 
shown in Fig. 109. In some cases, however, the holders are 
made to carry short bits broken from square bar stock and 
which are afterward sharpened into some resemblance to the 
true forged shape. (See Fig. 112.) 


MATERIALS FOR CUTTING TOOLS 

These are known as carbon steel (tool steel), high speed 
steel, and a product of the electric furnace sold under the 
trade name of “Stellite”. Carbon steel, or, as it was form¬ 
erly termed, “tool steel”, is high in carbon, eighty point to 
one hundred and twenty-five point, and when correctly 
heated and afterward plunged in cold water, hardens to a 
very high degree. Unfortunately for high speed cutting, the 
hardness is drawn at a comparatively low heat, and care 
must be taken not to overheat or blue it. 

High speed steel is a special steel having its composition 
alloyed with tungsten and sometimes vanadium or molyb¬ 
denum. While heat treatment does not give it the exceed- 
149 







THE 


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ing hardness of tool or carbon steel, high speed steel has the 
peculiar property of retaining its hardness at temperatures 
considerably in excess of those which readily soften tool steel. 
Tools made from high speed steel are used at speeds, feeds, 
and cuts which heat the tools and chips to a dull red. 

Stellite is a cutting material containing chromium, cobalt, 
and sometimes tungsten. It is cast into form and cannot be 
forged. Its hardness is practically equal to the diamond, and 
under favorable conditions marvelous turning may be done. 

MANDRELS 

Where the work is to be turned true with a hole through it, 
as, for example, gear blanks, etc., work centers must be pro¬ 
vided for holding it on the lathe centers. The common way 
is to force or drive into the work-hold a bar having center 
holes in its ends. This bar should be classed as a tool-room 
tool, and is properly known as a mandrel, although often 
called an arbor. 

A standard set of mandrels varies in diameter and in length, 
according to the shop conditions. They are made of either 
tool steel hardened and ground true with the centers, or from 
machinery steel, pack hardened and afterward ground. The 
ends for a short distance are reduced in diameter and pro¬ 
vided with flats for clamping on the dog. Mandrels usually 
taper at the rate of .0005" in an inch. The diameter of the 
hole fitted by the mandrel is stamped upon the larger end. 
As the quality of the work depends upon the truth of the 
mandrel it should be tested upon dead centers with a test 
indicator before being used. To use, drive or force it into 
place, using a mandrel press for forcing or a lead hammer for 
driving, carefully removing dirt, chips, or pieces of lead from 
the centers before placing the work in a lathe. Lathe drive 
with the usual lathe-dog, as for any job done on the centers. 
Avoid forcing or driving the mandrel into a hole that is 
neither round nor straight. Also avoid scoring the mandrel 
with the cutting tool. 


150 



F 0 R M OTOR MACHINISTS 


THREAD CUTTING ON A LATHE 

When screw threads are cut in an engine lathe, the point 
of the cutting tool is shaped to the exact form of the spaces 
between threads. By means of a lead screw and a train of 
gearing the tool is compelled to move along the axis of the 
work at a definite rate of advance as the work rotates. As 
the train of gears usually furnished with an engine lathe can 
be changed to give different rates of advance, it is in this 
manner possible to cut threads of a large variety of pitches. 
In practice, a set of several gears having different numbers 
of teeth are furnished with each lathe. Those furnished will 
usually provide for cutting all the threads within the range 
of the lathe with which they come. These are known as 
“change gears” and their use is obvious. 

Among the tools listed in Fig. 109 were shown ordinary 
threading tool points (Nos. 8, 9 and 12). The points shown 
have sides at an angle with each other of 60 degrees, but it 
is obvious that these or any other form of point must be 
formed and tested to give the correct form of thread desired 
in any particular case. 

Use lard oil when threading steel, wrought and malleable 
iron, and use plenty of lubricant. Cut the cast metals dry. 

Selecting Change Gears* 

Given—or having ascertained by use of a thread pitch 
gage—the number of threads per linear inch to be cut, and 
the number of threads per linear inch of the lead screw, the 
problem is to select gears giving the desired ratio of cut to 
lead screw. For example, it is desired that seven single 
threads per linear inch shall- be cut upon a 134 inch bolt, 
and it is found by scaling that the lathe lead screw had five 
single threads per linear inch. The ratio of cut to lead screw 
is then that of seven to five (7/5). The change gears selected 
should, therefore, be as seven is to five. If both members 
of a fraction are multiplied by the same number, the ratio is 
* See also pp. 162-168, Vol. I, Starrett Books. 

151 



STARRETT 


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not changed. This allows of raising the fraction to suit the 
gears which are in the set furnished; for example 

5 5 25 

If gears having thirty-five teeth and twenty-five teeth, 
respectively, are found in the furnished set, the selection of 
these gears will give, when rightly placed, the desired tool 
advance for cutting seven threads per linear inch. 

The directions above refer to the most simple form of 
lathe. Various lathe manufacturers have introduced dif¬ 
ferent arrangements of the gearing, and most lathes today 
have some form of quick change gear box, but with any lathe 
the above procedure will give correct results if it is first deter¬ 
mined what number of threads per inch will be cut if gears 
of the same number of teeth are placed on spindle stud and 
lead screw. This number called the “lathe screw constant” 
should then be considered as being the number of threads 
on the lead screw even though it is not the actual number. 
Most lathe manufacturers provide a table, attached to the 
lathe, which indicates at a glance the proper selection of 
gears for cutting threads of varying pitches. 


Placing the Change Gears 

The common engine lathe—if not equipped with the quick 
change gear box—has projecting through its headstock a 
shaft known as the “stud”. This projects a sufficient dis¬ 
tance to allow of mounting gearing and usually the upper 
cone for the feed belt. Gears- mounted or to be mounted 
upon this projecting stud are termed “stud gears”. Those 
mounted upon the projecting end of the lead screw are known 
as lead gears. When the number of threads to be cut is 
more per linear inch than that of the lead screw, the smaller 
of the selected gears is placed upon the “STUD” and the 
larger upon the lead screw. In the example given under 

152 



FOR MO TOR MACHINISTS 



Fig. 113 —Simple Train of Gears for Thread Cutting 


“Selecting Change Gears”, assuming that the stud rotates in 
unison with the lathe spindle, the 25-tooth gear would be 
placed on the stud and the 35-tooth gear on the lead screw. 
Reverse the order if the number of threads per linear inch 

153 




















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is less than that of the lead screw. The number of teeth in 
the large idler gear has no bearing upon the results, as it 
simply conveys the motion of the upper or stud gear to the 
lower or lead-screw gear. 


154 















F 0 R M O T 0 R MACHINISTS 


Compounding Gears 

As a means of enlarging the range of threads per linear inch 
possible to be cut with any set of change gears, most lathes 
are provided with an adjustable compound auxiliary stud 
which is provided with two locked gears having a ratio each 
to the other of two to one. As an example of their use, 
assume that a gear having ninety teeth was needed upon the 
lead screw to cut a given number of threads. If the set of 
gears furnished failed to provide a ninety gear, but did pro¬ 
vide one of forty-five teeth, placing this on the lead screw 
and meshing the two to one compound stud into the train 
completes the desired ratio, and advances the tool as if a 
90-tooth gear had been used. 

MEASURING AND TESTING SCREW 
THREADS 

For ordinary purposes, screw threads when cut are fitted 
to some threaded hole. This may be a hardened and ground 
gage, or may be an ordinary threaded nut, depending upon 
the accuracy of the work. Where the quality of the work 
demands special accuracy, or where standard thread gages are 
not available, the thread is tested by measurements made with 
calipers. If the point of the thread tool has been carefully 
and exactly formed and accurately set in place, measuring the 
diameter at the root of the thread may give sufficiently accur¬ 
ate results, and this may be done with a set of thin point 
spring calipers. (See Fig. 115.) When greater accuracy is 
required, micrometers having special thread-measuring points 
are resorted to. (See Fig. 116.) In all this it is assumed 
that the thread tool is ground, set, and operated to a given 
exact thread outline. 

MEASURING LATHE WORK 

Work done in the engine lathe is of such a variety that a 
considerable list of measuring tools may be needed to cover 
all cases. Ordinarily, however, the diameter measurements 
155 



THE 


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BOOK 



N9I79 


Fig. 115 —Outside 
Thread Calipers 


Fig, 116 —Thread Micrometer 
Caliper 


156 










FOR MOTOR MACHINISTS 


can be made with spring calipers, micrometers, or some of the 
usual bar calipers. Cylindrical plug and ring gages, as well 
as limit snap gages, are sometimes used for diameter measure¬ 
ments—especially on production work—and many of these 
may be used in measuring the shorter lengths. For the longer 
measurements of length, caliper squares are provided. The 
more accurate measurements are usually made by using a 
micrometer. 


TAPER TURNING* 

Where two parts are to fit firmly together when in use, as, 
for example, centers into lathe spindles, automobile shafts, 
etc., and it is desirable to have them easily removable, what 
are known as taper fits are used. For this purpose several 
rates of change in diameter have become standards. The 
B. & S. Standard is in general use for the spindle tapers in 
milling machines. The Morse taper is the one commonly 
used for all drills and drilling machinery. Either of these 
may be used for the tapered 
hole in lathe spindles, while 
some lathe manufacturers 
have established standards 
of their own. 

Ordinary tapers are rated 
at the amount which the 
diameter changes in a foot’s 
length; as, for example, the 
Brown Sc Sharpe taper of 
Y 2 inch per foot. To turn 
a taper it is necessary to 
use a lathe provided with a 
taper attachment or to ad¬ 
just the footstock of the 
engine lathe sufficiently off 
center to give the required 

* See also pp. 86-91, Vol. I, Starrett Books, and pp. 114-121, Vol. II, Starrett 
Books, % 

157 



Fig. 117 —Lathe Tailstock with 
Adjusting Screws 











THE 


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rate of diameter change. As all taper attachments are gradu¬ 
ated to read direct, they are easily set for the required taper. 
Adjustment of the tailstock of an engine lathe to turn a 
taper is not so simple as to use the taper attachment. 


TAPER TURNING WITHOUT TAPER 
ATTACHMENT 


If the distance the center points enter the work or the 
mandrel is ignored, the mandrel length can be considered as 
the distance apart of the center points. The calculation 
necessary to determine the distance which the centers shall 
be offset, is that of multiplying the length of the work or 
mandrel in feet by one-half of the required taper in inches. 
To turn a Brown & Sharpe taper on a piece of work 9 inches 
long the problem would work out as follows: 


. 500 

2 


X 


12 


= 0.1875 = 


_3_ 

16 


and the footstock would be set over. 3/16 inch. 

In the above illustrative example both length and amount 
of taper are given, but the amount of taper is not always 
known. Suppose a piece is 8 inches long and a taper is to 
be turned on one end, the tapered portion to be 4 inches 
long. The difference in diameters of these 4 inches is to be 
34 inch. How much must the tailstock be offset? If the 
taper is 34 inch in 4 inches it would be 134 inches in a foot 
and the tailstock would be moved over one-half of 134 inches 
or *34 inch, if the piece were a foot long, but as it is only 8 
inches or 2/3 of a foot long, the tailstock should be moved 
over 2/3 multiplied by % or 34 inch. Had the piece been 
18 inches long, it would have been necessary to move the 
tailstock over 1J4 (nr 3/2) multiplied by *34 or 1 34 inches. 

It has been assumed for these simple calculations that the 
lathe centers merely touch the ends of the piece, thus making 
the length of the piece the same as the distance between 
centers. But in actual work the distance the centers enter 

158 



F OR MO T 0 R MACHINISTS 


the piece must be considered. The calculation should be as 
accurate as possible to avoid continually changing the tail- 
stock to get a reasonably good taper fit. The necessity of 
considering the distance the center enters the piece depends 
somewhat upon its length. If the piece is very long, the 
actual taper will differ considerably from the calculated taper. 
If each center enters the piece one-fourth inch they would 
enter a total of one-half inch, and the length of the piece 
should be reduced by one-half inch in the calculation. While 
turning the taper the calipers should be used frequently so 
that it may be soon determined whether or not the tailstock 
is correctly placed. 



Fig. 118 —Lathe Set-up for Turning Taper without Taper 
Attachment 

Lathes adapted to taper turning without the use of a taper 
attachment have tailstocks which can be shifted off the dead- 
center line of the lathe spindle. On such tailstocks will be 
found two indicating lines marked zero, as shown in Fig. 117. 
If these markings are exactly aligned, the live spindle center 
of the lathe is in line with the tailstock center. 

To set the tailstock off center, it is only necessary to loosen 
one of the two set screws (F and G, Fig. 117) and screw in 
the other the same amount, or until it strikes the tailstock 
hub. Then clamp the tailstock to the bed and set up the 
work so that it occupies the position as shown in Fig. 118. 

The amount the tailstock shall be set off-center can be 

159 




























THE 


STARRETT 


BOOK 


determined only by the judgment of the machinist and will, 
of course, vary with the length of the taper, making it neces¬ 
sary to test the work by taking a light chip from the small 
end of the work and trying it in the taper socket to which 
the part is to be fitted. 

To test a taper, as in the case of an automobile shaft, it 
should be pressed lightly into a standard tapered hole and 
worked back and forth sufficiently to mark the places where 
bearing occurs. If the work has been lightly covered with 
some marking pigment, or with chalk, the bearing points 
will be more distinct. Care, however, must be taken that the 
coating is not sufficient to smooch, as it will deceive the work¬ 
man. Adjust taper-setting until a correct fit is obtained. 



Fig. 119 —Taper Turning Attachment on Lathe 

The use of a taper turning attachment, such as is shown 
in Fig. 119, greatly simplifies the work. The taper attach¬ 
ment illustrated, is fitted to the rear V of the lathe by two 
clamps, one at either end. A slide on the attachment 
regulates the degree of taper. The attachment is connected 
by an arm to the tool slide, which is then disengaged from 
its feed-screw. As the lathe carriage moves along the bed, 
the tool slide is moved in or out, according to how the slide 
of the taper attachment is set, thus guiding the cutting tool 
and producing the proper taper. Where the taper attach¬ 
ment is used, all that is required of the operator is to measure 
160 




















FOR MOTOR MACHINISTS 


AMOUNT OF TAPER IN A GIVEN LENGTH 

(Expressed in lOOOths of an Inch) 


•a 3 

ti, a 


Taper in Inches per Foot 


o 

14 

*4 

Vs 

X 

Vs 

X 

0.600 

% 

X 

1 

ix 

*4 

.1628 

.2441 

.3255 

.6510 

.9766 

1.302 

1.563 

1.628 

1.953 

2.604 

3.255 

14 

.3255 

.4883 

.6510 

1.302 

1.953 

2.604 

3.125 

3.255 

3.906 

5.208 

6.510 

3 4 

.6510 

. 9766 

1.302 

2.604 

3.906 

5.208 

6.250 

6.510 

7.813 

10.42 

13.02 

*4 

.9766 

1.465 

1.953 

3.906 

5.859 

7.813 

9.375 

9.766 

11.72 

15.63 

19.53 

X 

1.302 

1.953 

2.604 

5.208 

7.813 

10.42 

12.50 

13.02 

15.63 

20.83 

26.04 

54 

1.628 

2.441 

3.255 

6.510 

9.766 

13.02 

15.63 

16.28 

19.53 

26.04 

32.55 

Vs 

1.953 

2.930 

3.906 

7.813 

11.72 

15.63 

18.75 

19.53 

23.44 

31.25 

39.06 

14 

2.279 

3.418 

4.557 

9.115 

13.67 

18.23 

21.88 

22.79 

27.34 

36.46 

45.57 


2.604 

3.906 

5.208 

10.42 

15.63 

20.83 

25.00 

26.04 

31.25 

41.67 

52.08 

% 

2.930 

4.395 

5.859 

11.72 

17.58 

23.44 

28.13 

29.30 

35.16 

46.88 

58.59 

Vs 

3.255 

4.883 

6.510 

13.02 

19.53 

26.04 

31.25 

32.55 

39.06 

52.08 

65.10 

n 4 

3.581 

5.371 

7.161 

14.32 

21.48 

28.65 

34.39 

35.81 

42.97 

57.29 

71.61 

H 

3.906 

5.859 

7.813 

15.63 

23.44 

31.25 

37.50 

39.06 

46.88 

62.50 

78.13 


4.232 

6.348 

8.464 

16.93 

25.39 

33.85 

40.63 

42.32 

50.78 

67.71 

84.64 

Vs 

4.557 

6.836 

9.115 

18.23 

27.34 

36.46 

43.75 

45.57 

54.69 

72.92 

91.15 

,5 /fe 

4.883 

7.324 

9.766 

19.53 

29.30 

39.06 

46.88 

48.83 

58.59 

78.13 

97.66 

1 

5.208 

7.813 

10.42 

20.83 

31.25 

41.67 

50.00 

52.08 

62.50 

83.33 

104.2 

2 

10.42 

15.63 

20.83 

41.67 

62.50 

83.33 

100.0 

104.2 

125.0 

166.7 

208.3 

3 

15.63 

23.44 

31.25 

62.50 

93.75 

125.0 

150.0 

156.3 

187.5 

250.0 

312.5 

4 

20.83 

31.25 

41.67 

83.33 

125.0 

166.7 

200.0 

208.3 

250.0 

333.3 

416.7 

5 

26.04 

39.06 

52.08 

104.2 

156.3 

208.3 

250.0 

260.4 

312.5 

416.7 

520.8 

6 

31.25 

46.88 

62.50 

125.0 

187.5 

250.0 

300.0 

312.5 

375.0 

500.0 

625.0 

7 

36.46 

54. 69 

72.92 

145.8 

218.8 

291.7 

350.0 

364.6 

437.5 

583.3 

729.2 

8 

41.67 

62.50 

83.33 

166.7 

250.0 

333.3 

400.0 

416.7 

500.0 

666.7 

833.3 

9 

46.88 

70.31 

93.75 

187.5 

281.3 

375.0 

450.0 

468.8 

562.5 

750.0 

937.5 

10 

52.08 

78.13 

104.2 

208.3 

312.5 

416.7 

500.0 

520.8 

625.0 

833.3 

1042 

11 

57.29 

85.94 

114.6 

229.2 

343.8 

458.3 

550.0 

572.9 

687.5 

916.7 

1146 

12 

62.50 

93.75 

125.0 

250.0 

375.0 

500.0 

600.0 

625.0 

750.0 

1000 

1250 

13 

67.71 

101.6 

135.4 

270.8 

406.3 

541.7 

650.0 

677.1 

812.5 

1083 

1354 

14 

72.92 

109.4 

145.8 

291.7 

437.5 

583.3 

700.0 

729.2 

875.0 

1167 

1458 

15 

78.13 

117.2 

150.3 

312.5 

468.8 

625.0 

750.0 

781.3 

937.5 

1250 

1563 

16 

83.33 

125.0 

166.7 

333.3 

500.0 

666.7 

800.0 

833.3 

1000 

1333 

1667 

17 *» 

88.54 

132.8 

177.1 

354.2 

531.3 

708.3 

850.0 

885.4 

1063 

1417 

1771 

18 

93.75 

140.6 

187.5 

375.0 

562.5 

750.0 

900.0 

937.5 

1125 

1500 

1875 

19 

98.96 

148.5 

197.9 

395.8 

593.8 

791.7 

950.0 

989.6 

1188 

1583 

1979 

20 

104.2 

156.3 

208.3 

416.7 

625.0 

833.3 

1000 

1042 

1250 

1667 

2083 


Example: For the amount of taper in 33 Vs inches, when the taper is % inch 
per foot, add 1042 (for 20 inches) to 677.1 (for 13 inches) and 19.53 (for Vs inch); 
the result is 1738.63 thousandths, or 1.739 inches. 

161 

























THE 


STARRETT 


ROOK 


accurately the taper on the piece he wishes to duplicate or 
fit and set the slide to correspond. Remember that any 
taper actually set on the slide is doubled in the turning opera¬ 
tion. To illustrate: If in a distance of three inches measured 
accurately along the surface of the taper to be matched or 
fitted, it is found that the diameter of the piece or hole in¬ 
creases exactly 14 inch, then the taper attachment slide, 
measuring from the V-guides of the lathe, must be set to 
show a taper of Y inch in three inches of length. Even when 
using a taper attachment it is advisable to test the work— 
as was done when taper turning without the attachment— 
before the finish cut is taken. 

RULES FOR FIGURING TAPERS 


To Find 

Having Given 

Method 

Taper per inch. 

Taper per foot. 

Taper per foot. 

Diameter at small 
end, in inches. 

Diameter at large 
end, in inches. 

Amount of taper in 
inches. 

Distance in inches 
between two given 
diameters. 

Taper per foot. 

Taper per inch. 

End diameters and 
length of taper, both 
in inches. 

Diameter at large end, 
length of taper in 
inches, and taper per 
foot. 

Diameter at small end, 
length of taper in 
inches, and taper per 
foot. 

Taper per foot and 
given length in inches. 

Taper per foot ana the 
two diameters in 
inches. 

Divide by 12. 

Multiply by 12. 

Find difference between diameters; 
multiply by 12 and then divide by 
length of taper. 

Multiply taper per foot by length 
of taper and divide by 12; sub¬ 
tract result from diameter at large 
end. 

Multiply taper per foot by length of 
taper and divide by 12; add result 
to diameter at small end. 

Multiply given length by taper per 
foot and divide by 12. 

Find difference between diameters; 
multiply by 12 and then divide by 
taper per foot. 


ECCENTRIG TURNING 

While for the most part the lathe is used for work exactly • 
concentric with the axis, it can be used for turning work that 
is not concentric and which is termed “eccentric”. An ex¬ 
ample of such work is seen in the eccentrics which operate 
the valves of steam engines, and in crankshafts, etc. If the 
work has a hole through it, as in the above example, the hole 

162 









FOR MOTOR MACHINISTS 


CUTTING SPEEDS AND FEEDS FOR TURNING TOOLS 


High Speed Steel Tools; from Transactions A. S. M. E., 

Volume 28; F. W. Taylor. 

Cutting speed in feet per minute for a tool which is to last VA hours without 
regrinding. 


Inches 

Cutting Steel 

Inches 

Cutting Cast 

Iron 

Depth 



| Med. 

Hard 

Depth 





of Cut 

Feed 

Soft 

of Cut 

Feed 

Soft 

Med. 

Hard 

Standard %-inch Tool 

Standard M-inch Tool 



465 

233 

106 


W 2 

165 

82.5 

48. 1 


W2 

302 

156 

70. 9 


We 

118 

58.9 

34.4 

/32 

A 

209 

105 

47. 6 

Wi 

Vs 

81.3 

40. 7 

23. 7 

W2 

165 

82.8 

37. 2 


We 

65 

32. 5 

19 


Wi 

413 

207 

93. 9 


Wi 

151 

75. 5 

44 


W2 

277 

139 

62. 9 

Vs 

We 

108 

53.9 

31.4 

A 

% 

186 

92.9 

42. 2 


A 

74.4 

37. 2 

21. 7 

A 

123 

61. 6 

28 


We 

59.4 

29. 8 

17.4 


Wi 

350 

175 

79. 6 


W% 

134 

67. 1 

39. 1 


A 

235 

118 

53.4 


We 

95. 7 

47.9 

27.9 

3 /16 

We 

157 

78.8 

35.8 

We 

X 

66. 1 

33 

19.3 

W2 

125 

62.4 

28. 3 


We 

52. 9 

26.4 

15.4 


Wi 

313 

157 

71. 2 


W2 

124 

61.9 

36. 1 

X 

Wi 

210 

105 

47. 8 

A 

We 

88.4 

44. 2 

25. 8 

We 

141 

70.5 

32 

y 8 

61. 1 

30. 5 

17. 8 


Wi 

269 

135 

61. 3 


Wi 

111 

55. 6 

32.5 

% 

w% 

181 

90.4 

41. 1 

A 

We 

79.3 

39. 6 

23. 1 

We 

121 

60. 5 

27 


W2 

64 

32 

18. 7 

Standard 1-inch Tool 

Standard 1-inch Tool 


Wi 

490 

245 

111 


W2 

180 

90. 2 

52. 7 


Wi 

340 

170 

77.2 


We 

133 

66.4 

38. 7 

W2 

We 

235 

118 

53. 5 

3 32 

A 

94.5 

47. 2 

27. 6 

W> 

18Q, 

94. 6 

43 


We 

76.9 

38. 5 

22. 5 


A 

427 

214 

97. 2 


W2 

162 

81. 2 

47.4 


Wz 

296 

148 

67. 3 


We 

120 

59.8 

34.9 

a 

We 

205 

102 

46. 6 

A 

A 

85. 1 

42. 5 

24. 8 

Vs 

142 

71 

32. 3 


We 

69.3 

34. 6 

20. 2 


!4 

247 

124 

56. 2 


W2 

141 

70. 5 

41.4 


We 

171 

85. 6 

38. 9 


We 

104 

51. 8 

30. 2 

A, 

Vs 

119 

59.3 

26.9 

We 

A 

73.8 

36.9 

21. 5 

We 

95.4 

47. 7 

21. 7 


We 

60. 1 

30 

17. 5 


Wi 

314 

157 

71.4 


W2 

128 

64 

37.3 


W2 

218 

109 

49.4 


We 

94. 2 

47. 1 

27. 5 

X 

We 

151 

75.3 

34. 2 

A 

A 

67. 1 

33. 5 

19. 6 

Vs 

104 

52. 1 

23. 7 

We 

54. 6 

27. 8 

15.9 



265 

133 

60. 3 


Wi 

112 

56. 2 

32. 8 



183 

91.9 

41.8 


We 

82. 7 

41. 4 

24. 1 

H 

We 

127 

63. 6 

28. 9 

Vs 

A 

58.9 

29.4 

17.2 


3 A 

102 

51. 2 

23. 3 


We 

47. 9 

24 

14 



234 

117 

53. 2 


Wi 

103 

51. 4 

30 


W2 

162 

80.9 

36. 8 


We 

75. 6 

37. 8 

22.1 

A 

We 

112 

55.9 

25. 4 

V 2 

A 

53. 8 

26.9 

15. 7 

W2 

90 

45 

20. 5 


We 

43. 8 

21.9 

12. 8 


163 

































































































































THE 


STARRETT 


BOOK 


is first finished to required dimensions. A mandrel is then 
used for carrying the work on the centers. While the mandrel 
has been built on one set of centers exactly true with its axis, 
for eccentric turning it has a second set of centers which are 
offset the amount required for the eccentricity specified. In 
the case of eccentrics made solid with the shaft, the two sets 
of centers, one for turning the shaft and the other for finish¬ 
ing the eccentrics, are made side by side in the ends of the 
shaft, as shown in Fig. 120. 



When the specified eccentricity is too extreme to allow both 
pairs of centers coming within the limits of the diameter of 
the shaft, special ends may be cast or forged on the ends of 
the work, and can afterward be machined off. In crank¬ 
shaft turning, special attachments are provided for the ends 
of the shaft. Special eccentric turning chucks also may be 
made to hold the work. 

CHUCKING 

Chucking includes not only the mounting of the work in 
the chuck, but performing the necessary operations on it 
while so held. The name “chuck” is given to devices having 

164 

























FOR MOTOR MACHINISTS 


a variety of forms, all of which are designed to hold work 
or tools upon or in the nose of a spindle. In general, the 
heavier sorts are mounted upon a face-plate which screws 
upon the end of the spindle, while smaller sizes are fitted with 
a taper shank which fits tightly into the tapered hole in the 
spindle. These smaller sizes are used for carrying tools such 
as drills, screws, studs, wire pins, etc., and are known as 
drilling and spring chucks. 

The larger sizes are widely used for holding work for 
machine operations, and are sometimes called “work-chucks”. 
On their face they are provided with adjusting jaws movable 
regularly to and from the center; these jaws are so designed 
that a considerable variety of work may be readily held and 
successfully worked upon with common cutting tools. If the 
jaws are moved by means of screws or gears, and can be 
adjusted independently, the chuck is called an independent 
jaw-chuck. If all the jaws are made to move together, it 
is known as a Universal chuck. 

Holding the Work 

The work must be clamped firmly in the chuck while 
being machined. Care must also be taken that the clamp¬ 
ing of a slender piece is not so firm as to distort or spring it. 
If work slips, tools may be broken, and if held too tightly 
and sprung or crushed, the work is injured and in some cases 
entirely ruined. 

Truing the Work 

Adjusting the chuck-jaws so that the work will run as true 
as desired is termed “truing up the work”. This is pre¬ 
liminary to any tooling which may be done on the job. Often 
this truing of the work can be accomplished by holding a 
piece of chalk to just touch the work, leaving a plain marking. 
Where greater accuracy is required, the work is indicated 
with a Universal Dial Test Indicator or Universal Test 
Indicator. 


165 



THE 


STARRETT 


ROOK 


KNURLING 

The surfaces of adjusting screws and small machine parts 
are often given a regular rough surface for easy gripping. 
In the machine shop this is done by using a tool known as a 
“knurl” or “knurling tool”, which consists of one or more 
indented rollers or knurls mounted to rotate in some form 
of holder. 

These knurls are forced into and fed along the stock until 
the indented design has been sufficiently imprinted into the 
surface. When neatly and effectively done the results give 
a fine gripping surface and a rather pleasing effect to the eye. 
The knurling tool may be fed along the surface of the work 
by hand, but usually the power traverse feed is used. The 
process is repeated if one passage of the tool does not give 
sufficient depth. 

LAPPING 

Round work that is to run in bearings and bushings such 
as crankshafts, propeller shafts, etc., must be finished to a 
smooth, true surface after having been turned to size. For 
this purpose a lap is used. A lap consists of any kind of 
device desired that will clamp around the shaft and hold 
some fine grinding compound while the work revolves. The 
most simple form of lap is made by hinging two pieces of wood 
together, cutting a recess for the shaft and filling this in with 
old pieces of belt leather. A mixture of oil and grinding 
compound is then put on the leather, the lap clamped on the 
shaft and the shaft turned until it has the desired polish. Off- 
center parts such as the crankpins can be done very easily if 
the lathe is placed in back gear so that the work runs slowly. 
The lap should move back and forth as the work turns around. 

LATHE WORK 

So many special purpose machines have been developed for 
automobile service that the uni versatility of the lathe is some¬ 
times lost sight of by those who have not learned the machin- 
166 



FOR MOTOR MACHINISTS 


ist’s trade. Very often an otherwise impossible boring job 
can be done on a lathe with a boring bar which is simply a 
steel bar of sufficient diameter so that it will not spring and 
is provided with centers and a flat end for the attachment of 
the lathe-dog. At convenient points there are square holes 
through the bar to accommodate the self-hardening steel 
cutters. These are held in place with set screws. By clamp¬ 
ing the work done on the lathe carriage in exactly the right 
position, the boring bar cutters cut a hole the size they are 
set for, the rod or screw being used for the feed. The cross 
slide on the lathe is usually removed when using a boring bar. 

When truing long thin work it is best to use the steady 
rest which is part of the lathe equipment. This keeps the 
work from springing and helps to get it true. 

By fitting a drill pad to the tailstock in place of the center 
and holding the drill in a chuck on the headstock, it is pos¬ 
sible to use the lathe as a drill press for some kinds of work. 

Lathes can be fitted with milling attachments for cutting 
keyways, grinding attachments for doing cylindrical grind¬ 
ing and numerous other fittings. 

MILLING AND MILLING MACHINES* 

Among the machine tools which should form part of the 
equipment of every motor repair shop, none is of greater 
convenience or more important than the Universal Milling 
Machine. Its range and adaptability to motor service shop 
work is suggested by the following partial list of operations 
which are efficiently performed on this machine: Drilling 
operations on yoke, fork or spring hanger; turning and cut¬ 
ting off pins and king bolts; milling threads on shafts a,nd 
axles; boring wrist-pin holes in cylinders; boring and reaming 
cylinders; milling keyways and oil grooves; milling hexagon 
and square shafts; milling multiple splined shafts and axle 
ends; cutting differential bevel gears; milling timing and 
rotary pump gears; cutting chain sprockets, splining tapered 

* See also pp. 99-100, Vol. I, Starrett Books, and pp. 81-88, Vol. II, Starrett Books. 

167 



THE 


STARRETT 


BOOK 


holes by using a slotting attachment, etc., etc. A very large 
percentage of all the machine tool work called for in motor 
repair shops can be done to advantage on a universal milling 
machine. 

The standard milling machine is of column and knee type. 
The knee, which carries the work table, is mounted on the 
column and can be adjusted vertically to bring the work into 
proper position for the milling cutters to operate. It may 
also be fed upward to take vertical cuts. The work table, 
mounted on the knee, is fed horizontally in two directions, 
one at right angles to the axis of the spindle, and the other 
parallel to the spindle axis. The cutterhead on one type of 
Universal miller that is deservedly popular with the automo¬ 
bile repair trade may be rotated to cut at any angle through 
90° in a plane parallel to the axis of the column, and by use 
of a sub-head, may be swung through 270°. The sub-head, 
in turn, may be turned through 360° in a plane at right angles 
to the main cutterhead. This combination infinitely in¬ 
creases the variety of cuts possible with a single right angle 
end mill and makes a corresponding reduction in tool costs. 
It should be noted that while in lathe work the cutting tool 
is fixed and the work rotated against it, in a milling machine 
the work is fixed and a rotating cutter is brought in contact 
with it. 

Milling machines are usually belt driven from countershaft, 
and the changes of speed obtained by belt shifting are sup¬ 
plemented by additional changes obtained through series of 
gears within the miller itself. Feeds, both longitudinal and 
transverse, are controlled by wheels or levers on the miller. 
Longitudinal feed of the table, or travel of the saddle, is in 
a direction at right angles to the axis of the spindle. Trans¬ 
verse or cross feed is movement of the saddle in or out on 
the knee in a direction parallel to the axis of the spindle. 
Vertical feed is the movement of the table and saddle ver¬ 
tically in a direction parallel to the axis of the column. 

For purposes of illustration the Van Norman Duplex Mill- 

168 




Fig. 121—Duplex Milling Machine 


1 . 

2 . 

3. 

4. 

5. 

6 . 

7. 

8 . 
9. 

10 . 

11 . 


Sliding Ram 12. 

Swivel Cutter Head 13. 

Over-Hanging Arm 14. 

Arm Head 15. 

Milling Cutter 16. 

Arm Head Center 17. 

Table 18. 

Saddle 19. 

Over-Hanging Arm Strap Block 20. 

Cross Feed Screw Hand Wheel 21. 

Knee Elevating Screw Handle 22. 

169 


Knee 

Knee Elevating Telescope Nut 

Arm Straps 

Main Driving Pulley 

Tool Tray 

Sliding Ram Handle 

Chain Guard and Sprocket 

Feed Box 

Table Feed Screw 

Knee Gib Binders 

Column 


























































































































































































































































THE 


STARRETT 


BOOK 


ing Machine has been selected because it so completely meets 
the needs of the motor repair man. The designations of its 
parts are shown in Fig. 121. 


MILLING KEYWAYS AND SPLINES* 



In milling straight or standard keyways the vise 
is clamped on the milling machine table with its 
tongues in the bottom slot 
and its jaws parallel with the 
table ways, the shaft being 
held in the jaws of the vise 
(Fig. 122). In the case of a 
Ford axle shaft, which re¬ 
quires a keyway in its taper 
end, the axle must be clamped 
in the vise at the angle so 

that the top side of the taper is level horizontally. Use a 
surface gage in setting up the work to be sure that it lines 
up. The type of key way cutter used on this job is carried 
in a collet in the nose of the spindle. 


Fig. 122—Milling Straight or 
Standard Keyway on Tapered 
Shaft 



Fig. 123 —Cutting Woodruff Keyway 


Woodruff keyways are very common in motor replacement 
parts. The set-up is the same as for milling a standard key¬ 
way, but the cut is made by feeding the cutter vertically 
into the work. (See Fig. 123.) 

* See also pp. 45-51 and p. 88, Vol. II, Starrett Books. 

170 











FOR MOTOR MACHINISTS 


STANDARD KEYWAYS FOR CUTTERS 
AND ARBORS 



Diameter of Hole (D) 
in Cutter, Inches 

Width (W) 
Inches 

Depth (A) 
Inches 

Radius (R) 
Inches 

% to % 

V 

Vi 

.020 

H to % 

Vs 

Ve 

.030 

Ve to iy 

% 

V 

.035 

i Ve to i y 8 

Ve 

Vi 

.040 

*1 Veto ly 

M 

H 

.050 

*V% to 2 

Ve 

% 

.060 

2 Ve to 2 

H 

Ve 

.060 

2 % to 3 

Ve 

Ve 

.060 


* For all Gear Cutters of IV inch, 1% inch, 2 inch diameters, use Ve inch, 
% inch, V inch keys, respectively; iy 2 inch uses also % inch key. 


TEETH IN MILLING CUTTERS 


Diameter of 
Cutter, Inches 

Ni 

Plain 

Roughing 

Cutter 

imber of Te( 

Side 

Cutter 

;th 

Plain 

Cutter 

Rad ius of 
Point of 
Plain Flut¬ 
ing Cutter 

Width of 
Land 
on Teeth 

2 and 2y . 

8 

22 

18 

Vi 

Vi 

2V 2 and 2M . 

8 

24 

18 

Vi 

V 

3. 

8 

24 

18 

Vi 

Vi 

sy . 

9 

24 

18 

7 / 

/64 

Vi 

3% and 4 . 

9 

26 

20 

y 

Vi 

4H .. • 

10 

26 

22 

y 

Vi 

5. 

10 

28 

22 

Vi 

Vi 

5V 2 . 

11 

28 

24 

Vi 

Vi 

6 and &y . 

12 

30 

24 

Vi 

Ve 

7 and 7% . 

14 

30 

26 

Ve 

Ve 

8 .. 

16 

30 

26 

Ve 

% 

sy . 

16 

32 

26 

Ve 

% 

9 and 9y . 

18 

32 

30 

Ve 

V 

10. 

20 

32 

30 

Ve 

% 


Angle of Cutter for Side Teeth; For cutters over y inch wide, 70° or 75° angle; 
for cutters y inch wide and under, 80° angle, or 85° in extreme cases. 


171 













































THE 


STARRETT 


ROOK 


WOODRUFF KEY SIZES 


No. 

Length 

Thickness 

Type 

Cutter 

Diameter 

0 

X 

Vo 

Half circle 

X 

00 

Vo 

Vi 

Half circle 

Vo 

000 

Vs 

Vs 

Half circle 

Vs 

1 

X 

Vo 

Flat bottom 

X 

2 

X 


Flat bottom 

X 

3 

X 

Vs 

Flat bottom 

X 

4 

X 

Vi 

Flat bottom 

Vs 

5 

Vs 

Vs 

Flat bottom 

Vs 

6 

Vs 

% 

Flat bottom 

Vs 

61 

Vs 

Vo 

Flat bottom 

Vs 

7 

X 

Vs 

Flat bottom 

X 

8 

X 

Vi 

Flat bottom 

X 

9 

X 

Vo 

Flat bottom 

X 

91 

X 

X 

Flat bottom 

X 

10 

Vs 

Vi 

Flat bottom 

Vs 

11 

Vs 

Vo 

Flat bottom 

Vs 

12 

Vs 

V 

Flat bottom 

Vs 

A 

Vs 

X 

Flat bottom 

Vs 

121 


X 

Flat bottom 

Vs 

13 

1 

Vo 

Flat bottom 

l 

14 

1 

Vi 

Flat bottom 

1 

15 

1 

X 

Flat bottom 

1 

B 

1 

Vo 

Flat bottom 

l 

152 

1 

Vs 

Flat bottom 

l 

141 

61 A 

X 

Flat bottom 

1 

131 

'Vo 

Vo 

Flat bottom 

1 

16 

1 X 

Vo 

Flat bottom 

IX 

17 

1 Vs 

Vi 

Flat bottom 

Ws 

18 

1 Vs 

X 

Flat bottom 

IX 

C 

1 Vs 

Vo 

Flat bottom 

1 Vs 

161 

1 

Vo 

Flat bottom and ends 

IX 

19 

1 X 

Vo 

Flat bottom 

IX 

20 

1 M 

Vi 

Flat bottom 

IX 

21 

i X 

X 

Flat bottom 

ix 

D 

1 X 

Vo 

Flat bottom 

ix 

E 

l X 

Vs 

Flat bottom 

ix 

22 

l X 

X 

Flat bottom 

1 x 

23 

1 Vs 

Vo 

Flat bottom 

l H 

F 

l X 

Vs 

Flat bottom 

IVs 

24 

i X 

X 

Flat bottom 

IX 

25 

l X 

Vo 

Flat bottom 

IX 

G 

i X 

Vs 

Flat bottom 

IX 

126 

1 Vs 

Vo 

Flat bottom and ends 

2Vs 

127 

l X 

X 

Flat bottom and ends 

2Vs 

128 

i X 

Vo 

Flat bottom and ends 

2Vs 


172 













FOR MO TOR MACHINISTS 


WOODRUFF KEY SIZES (Continued) 


No. 

Length 

Thickness 

Type 

Cutter 

Diameter 

129 

1 Vs 

Vs 

Flat bottom and ends 

2Vs 

26 

1 2 % 

% 

Flat bottom and ends 

2V 8 

27 

1 2 ^2 

X 

Flat bottom and ends 

2 y 8 

28 

1 2 % 

% 

Flat bottom and ends 

2 V a 

29 

1 2 '32 

Vs 

Flat bottom and ends 

2Vs 

Rx 

2 

X 

Flat bottom and ends 

2X 

Sx 

2 

% 

Flat bottom and ends 

2M 

Tx 

2 

Vs 

Flat bottom and ends 

2V 

Ux 

2 

tie 

Flat bottom and ends 

2X 

Vx 

2 

X 

Flat bottom and ends 

2X 

R 

2% 

X 

Flat bottom and ends 

2 X 

S 

2 X 

% 

Flat bottom and ends 

2X 

T 

2 Va 

Vs 

Flat bottom and ends 

2X 

U 

2% 

X 

Flat bottom and ends 

2X 

V 

2% 

X 

Flat bottom and ends 

2X 

30 

2Vs 

X 

Flat bottom and ends 

SX 

31 

2 Vs 

X 

Flat bottom and ends 

SX 

32 

2Vs 

X 

Flat bottom and ends 

SX 

33 

2 Vs 

X 

Flat bottom and ends 

sx 

34 

2 Vs 

Vs 

Flat bottom and ends 

sx 

35 

2Vs 

n /fe 

Flat bottom and ends 

SX 

35 

2 Vs 

X 

Flat bottom and ends 

SX 


Woodruff keys are furnished in three grades: 1, special 
carbon steel; 2, special carbon steel heat treated; and 3, 
nickel steel heat treated. The nickel steel keys have a dis¬ 
tinguishing line rolled along the top. Keys and cutters 
correspond in size and number with the following exceptions: 


For Key No. 

Use Cutter No. 

For Key No. 

Use Cutter No. 

121 

A 

129 

29 

141 

15 

Rx 

R 

131 

B 

Sx 

S 

161 

C 

Tx 

T 

126 

26 

Ux 

U 

127 

27 

Vx 

V 

128 

28 




Keys should project above the shaft one-half their thick¬ 
ness. To remove the key, tap it on one end until it rocks, 
when it can be pulled out. 


173 




























THE 


STARRETT 


ROOK 


Whenever possible, mill key ways with a splining cutter, 
as this method permits the use of heavier feeds and conse¬ 
quently requires less time. The 
set-up is the same as before, 
but the cutter is carried on an 
arbor, supported at its outer 
end by a pendant from the 
overarm. (See Fig. 124.) 

For milling special keyways 
for which no proper cutter is 
to be had, a fly-cutter may 
be used as shown in Fig. 125. 
The fly-cutter consists of a 
lathe tool-bit ground down to 
the width of the keyway re¬ 
quired and held in a fly-cutter arbor, chucked on the spindle. 
When using a fly-cutter the feed must be reduced to cor¬ 
respond to the difference between the single cutting tooth 
of the fly-cutter and the dozen or more cutting teeth of an 
ordinary milling cutter. 

Certain keyways must be cut with an end mill, as shown in 
Fig. 126. In this operation the swivel vise is set up on the 
machine table and the work clamped as shown in the illus¬ 
tration. The vise is then swung sufficiently to align the 



Fig. 124 —Milling Keyway 
with Splining Cutter 
















FOR MOTOR MACHINISTS 

taper of the shaft with the table ways. The cutter is started 
at one end of the keyway and, using the horizontal feed, is 
allowed to travel the entire length of the keyway required. 
Returned to the starting point, the cutter is fed into the work 
a little deeper and the operation repeated. 

For cutting a key way in a taper hole a slotting attachment 
should be used as shown in Fig. 129. Spur gears and other 
parts requiring only a single keyway can be clamped to the 
table of the milling machine and the keyway cut with the 
slotting attachment set in a vertical position. 


SPLINE MILLING 



Fig. 127 —Set-up for Cutting Fig. 128 —Spline Milling with 
Spline Fly-Cutter 


Milling multiple splines calls for a very considerable degree 
of accuracy and skill. The operation schedule is as follows: 
Set a pair of milling cutters, spaced to the required key width, 
on the milling machine arbor, as shown in Fig. 127. This 
setting should be done to micrometer measurements. Then 
mount the work on the dividing head and tailstock centers. 
Set the space for the first spline exactly over the center of 
the shaft. To accomplish this, move the face of the cutter 
so that it barely touches the work. Drop the table holding 
the work away from the cutter. Knowing the thickness of the 
cutter in thousandths of an inch, move the platen holding the 
work, by means of the cross-feed, so that exactly one-half 
the diameter of the cutter is in alignment with the periphery 
175 




THE 


STARRETT 


ROOK 


or surface of the work. Continue to move the platen, by 
means of the cross-feed, a distance exactly equal to one-half 
the diameter of the work. The milling cutter will then be in 
exact center. After setting the dividing head, index for the 
required number of splines and raise the work up to the cutter 
and depth required. Put on the longitudinal feed and mill 
the full length of the spline. 

After the first cut withdraw the work by means of the quick 

traverse on the longitudinal 
travel and index to the next 
spline. Repeat until all 
splines are cut equally spaced 
and the work is ready for cut¬ 
ting the bottom of the splined 
grooves to the proper radius. 

Now remove the arbor and 
cutter gang and push the 
overarm out of the way. In 
the spindle, insert a fly-cutter 
arbor carrying a tool-bit 
ground on the end with a 
radius equal to the diameter 
of the spline shaft. (See Fig. 
128.) Set the work so that 
the cutter, as it rotates, will 
remove the metal in the 
operation. 



Fig. 


129 —Cutting Keyway in 
Tapered Hole 


splines left by the previous 


SHAPERS 

Although many of the operations that were formerly done 
with shapers are now performed on milling machines, and 
although the latter has a much wider range of work than 
could possibly be done with a shaper, nevertheless, a small 
shaper—say one with a 16-inch stroke—will justify its being 
included in the equipment of any auto repair shop that seeks 
to handle all classes of repair work economically. 

176 



























FOR MOTOR MACHINISTS 

The shaper, like the milling machine, or the planer, is in¬ 
tended to remove metal from flat surfaces as contrasted with 
the round work done on a lathe or cylindrical grinder. In 
the shaper, the work is mounted in a fixed, work-holding 
vise, while the cutting tool is carried in a tool-post mounted 
at one end of the reciprocating shaper head. The work is 
moved laterally by either power or hand feed and the tool 



Common Type op Shaper 
177 

























































































































THE STARRETT ROOK 


holder is raised or lowered to the proper depth of cut. The 
tool holder or post, is so mounted on an index that it may¬ 
be set at any convenient angle. 

GRINDING* 

More and more, motor repair shops are using grinding 
machines in finishing operations on motor parts. Cylinder 
blocks, crankshafts, pistons, wrist pins, crank pins, valve 
stems and faces, rear axles, drive shafts, king pins, etc., are 
among the work now often finished on the grinding machine. 
Savings in time and labor as well as closer, more accurate work 
are responsible for the change, together with the fact that the 
grinding machine is more of an all-purpose tool than is any 
other machine tool with the possible exception of the lathe. 

In the machine shop the term “grinding’' refers to the pro¬ 
ducing of finished surfaces by means of rotating grinding 
wheels, and the process of grinding as used in finishing ma¬ 
chine parts is today the most efficient method devised for 
the purpose. Grinding machines are classified into two 
groups, (a) those for curved surfaces; as, for example, cyl¬ 
indrical work; and (b) those for plane or flat surfaces. The 
first of these is usually called a cylindrical grinder, and the 
second is known as a surface grinder. Each group has many 
designs, made necessary by the varied uses to which grinding 
is adapting itself. 

Grinding Wheels 

These are now known as abrasive wheels, and the material 
from which they are made is termed an abrasive. The 
abrasives in common use are the minerals emery and co¬ 
rundum, and the manufactured abrasives, sold under the 
trade names of Alundum, Aloxite, Carborundum, Cry stolon. 
Owing to the uniformity of the product as it comes from the 
electric furnace, manufactured abrasives are at present more 
largely used than natural abrasives. 

*See also pp. 109-118, Vol. I, Starrett Books, and pp. 35-39, Vol. II, Starrett 
Books. 

178 



FOR MOTOR MACHINISTS 


Abrasive Wheels 

An abrasive wheel is made up of one of the above-named 
ABRASIVES and a BOND. The bond is, as its name indi¬ 
cates, something for holding the abrasive in mixture. Grind¬ 
ing wheels are made by three processes, known as Vitrified, 
Silicate and Elastic. 

Vitrified Wheels 

In wheels made by the Vitrified process, the bond is of 
earth or clay which hardens or vitrifies when subjected to a 
temperature of about 2500° F. to 2800° F. for a definite 
period of time. Various grades of hardness are obtained by 
using bonds of different tensile strength. The ideal bond is 
one which retains the grains of abrasive until sufficiently 
dulled by use, and then allows them to break away, bringing 
fresh cutting edges and points into grinding contact. 

Silicate Wheels 

Silicate of Sodium is the bond used in silicate wheels, and 
wheels made by this process are most efficient for tool and 
knife grinding. Elast ; c Wheels 

This process of bonding is generally used for the very thin 
wheels used for slitting metals. The principal ingredient of 
the bond is shellac. 

Grading the Abrasive 

By numerous crushing, grinding, cleansing and sorting pro¬ 
cesses, the abrasive is graded into a series of sizes which give 
the wheel its grain number. This number conforms to the 
sieve mesh through which the abrasive is passed; for example, 
grain No. 40 indicates that the abrasive was graded through 
a sieve having a mesh of forty to the linear inch. 

Combination Wheels 

For many grinding purposes the combination wheel is pre¬ 
ferred to a wheel of single grade. Combination wheels are 
made up of abrasives of several grain numbers. 

179 



THE 


STARRETT 


ROOK 


Bonding 

The ideal bond is one which is impervious to moisture, 
does not soften by heat, and which holds firmly the cutting 
points of the abrasive until they become dulled by use. The 
bond then releases the dull abrasive and permits fresh, sharp 
points to begin cutting. With abrasives of equal quality 
the maker who nearest approaches the ideal bond produces 
the superior wheel. 

Grading the Wheels 

In grinders’ language, abrasive wheels are known as hard 
wheels and soft wheels. The maker, therefore, lists his wheels 
as hard or soft by some scale of numbers or by letters. A 
prominent firm uses the letters of the alphabet, as shown in 
the following list in which “M” is medium. 


Norton Grade List 

The following grade list is used to designate the degree of 
hardness of Norton Vitrified and Silicate Wheels, both Alun- 
dum and Crystolon. 


Soft 


Medium Soft 


MEDIUM.M 


MEDIUM 


Medium Hard.Q 


Hard...U 


W 


Extremely Hard .V 


The intermediate letters between those designated as soft, 

180 










FOR MOTOR MACHINISTS 


medium soft, etc., indicate so many degrees harder or softer; 
e.g., L is one grade or degree softer than medium; O, two 
degrees harder than medium, but not quite medium hard. 

Elastic Wheels are graded as follows: 1, 2, 23^, 3, 4, 

5, and 6. Grade 1 is the softest and grade 6 is the hardest. 


Cylindrical Grinding 

When the piece being ground is rotated, the process is 
known as cylindrical grinding, and the development of ma¬ 
chines for grinding cylinders has given the process a great 
impetus. While it is possible to grind from the rough stock 
without previous lathe work, the method usually followed is 
to first rough turn the work. 


Roughing for Grinding 

This process includes the work done in removing excess 
stock previous to finishing to size in the grinding machine. 
Unless a study is made of the conditions surrounding the 
whole operations of the lathe and the grinding machine, lack 
of efficiency may result. In general, where the work is to 
be ground, it is best to consider the lathe as a mere rough¬ 
ing machine for removing the excess of stock at as deep a 
cut and as coarse a feed as is consistent with an efficient 
cutting speed, leaving the job of finishing to the grinding 
machine. 


Amount to Leave for Grinding 

If the grinding machine is modern in design, as much as 
1/32 of an inch, or even more, may be left on machine steel 
parts for removal in the grinder, the amount varying with 
the size of the work itself and is largely determined by the 
judgment and skill of the operator. An allowance of 1/64 of 
an inch is general on the smaller machine parts, but this 
allowance should be increased on larger sizes. 

181 



THE 


STARRETT 


BOOK 


Selecting the Wheel 

The selection of the wheel to be used in any grinding opera¬ 
tion can, perhaps, best be made by reference to the tables 
in this chapter, which fairly represent general practice. As 
the hardness of material and the area of contact made by 
the wheel have a marked influence, no table can entirely 
solve the problem, but it may be used as a start in the right 
direction. In general, a soft wheel should be used on hard¬ 
ened work and a harder wheel on soft materials. 

In selecting a wheel for a job the following simple rules and 
suggestions may be of assistance: 

Use wheels of the aluminous abrasive—or vitrified—type 
for materials of high tensile strength and hardness, such as 
steel. For materials of low tensile strength, such as cast 
iron, brass, bronze, aluminum, etc., use wheels of the silicate 
—or silicon carbide—type. 

The more rigid the machine and the less vibration there is, 
the softer the wheel which may be used, and vice versa. 

The narrower the line of contact between the work and 
the wheel, the harder the wheel must be. 

While due allowance must be made for the personal factor 
of the operator, the condition of the grinding machine and the 
peculiarities of any particular job, a 36-H or 36-1 Crystolon 
or Carborundum w heelrunning at approximately 4500 s.f .p.m. 
(surface feet per minute) will usually be found to be correct 
for cylinder grinding. For crankshaft grinding on bearings 
and pins, and for wrist pins, valve faces, rear axles, drive 
shafts, king pins, etc., a 6646-K Alundum wheel, running at 
6000 to 6500 s.f.p.m., may be used to advantage. Where 
there are only a small number of valve stems to be ground, or 
for the casual job of this type, the same wheel may be used, 
but for a large number a 6646-M wheel will be found more 
economical. For general tool grinding in motor repair work 
a 6646-L or 6646-M wheel, running at about 5000 s.f.p.m., 
is recommended. 


182 



FOR MOTOR MACHINISTS 


MOUNTING THE WHEEL 

The wheel should be so mounted that there are no unequa 
stresses set up. Suitable guards should be provided to pre¬ 
vent injury to the workmen in case of the wheel bursting. 
Figure 130 shows RIGHT and WRONG methods of mount¬ 
ing wheels—carefully study the cuts. 



Fig. 130 —Right and Wrong Methods of Mounting Wheel 


MEASURING THE WORK 

The need for micrometers for obtaining exact measurements 
is nowhere better illustrated than in grinding. Fig.. 131 
shows an operator adjusting his micrometer for obtaining a 
measurement on a cylindrical piece. While in lathe work 
the position of the operator leads naturally to^ adjusting 
the micrometer spindle with the fingers of the right hand, 
183 









































THE 


STARRETT 


ROOK 


the left hand grasping the frame, in grinder work the reverse 
is generally true, hence he occupies the position as shown. 

GRINDING FLAT SURFACES 

Flat surface grinding may be divided into two general 
classes: (a) Machine parts, such as boxes, tables, cross-slides, 
faces of nuts, etc.; and (b) fine tool, work, as, for example, 
steel blades, scales and rulers, straight edges, etc.. Until 
recently the first-named class of work was done by reciprocat- 



Fig. 131—Using Micrometer on Grinding Machine Work 

ing the work beneath the circumferential face of an abrasive 
wheel in a machine which, in principle, is not unlike a small 
planer. The use of machines with CUP WHEELS has prac¬ 
tically revolutionized such grinding, and an exactness of 
surface is being obtained on fine flat work which leaves little 
to be desired. 

The operator probably has a much closer control of the 
cutting speed on a grinding machine than on any other 
machine tool because not only can the grade—or degree of 
hardness—of the wheel—equivalent to the cutting tool—be 
184 









FOR MOTOR MACHINISTS 


changed, but also speed changes may be made in both the 
work and wheel revolutions. Slowing down the work revolu¬ 
tions, leaving the wheel turning at the same speed—produces 
a harder acting wheel and vice versa. 

It is often claimed—and properly—that a wheel cuts better 
after it has been partly worn down. The reason is—kept at 
the same s.f.p.m.—because of the wheel's diameter, each 
cutting particle in its surface has more work to do and the 
wheel acts “softer”. A soft wheel will always do more work, 
cut freer and use less power than a hard wheel and requires 
no forcing or crowding into the work to make the wheel face 
sharp. Another reason for a wheel's improving in cutting as 
it wears away, is that the arc of contact of the wheel with the 
work has been reduced and with the smaller diameter of the 
wheel the depth to which the cutting particles in the wheel 
are buried in the work is increased. This causes a greater 
strain on each cutting particle with the result that they are 
more quickly torn from their setting, keeping a fresh, un¬ 
glazed surface in contact with the work at all times and also 
still further reducing the diameter of the wheel. 


GRAIN NUMBERS COMMONLY USED IN VARIOUS 
POLISHING OPERATIONS* 


Aluminum—120-150-180. 

Auto Parts—24-36-60-70-80-90-120-150. 
Auto Springs—36-54-70. 

Bicycle Parts—70-80-90-120-150. 
Brass—36-60-70-80-90-120-150. 
Carriage Hardware—36-46-54. 

Cast Iron—54-60-70-80-200-F-FF-FFF. 
Dies—60-80-90. 

Edge Tools—36-54-60-70-80-90-120-150 
-180. 

Electric Starter Parts—24-36-60-90-120 
-150-180. 

Forgings—36-46-54-60-70-80-90. 

Glass (Beveling)—90-120-150. 

German Silver—100-F. 

Hammers—46-54-60-70-80-90-120-180. 
High Speed Steel—36-70-80. 

Knives—12-14-20-36-46-54-60-70-80- 
90-120. 


Lapping Bushings—90-150-180-FFF. 
Lapping Gages—65-F. 

Lapping Machine Parts—200-FFF. 
Lapping Steel Balls and Bushings—F- 
FFF. 

Lapping Valves—FFF. 

Monel Metal—F. 

Machine Parts—54-60-70-100-120-150- 
F. 

PI iers—46-54-60-70-80-90-100-120. 
Renewing Files—36. 

Saws—60-70-80-90-120-F-FF-FFF. 
Screws—46-60-70-80-90. 

Spark Plugs—80-120-F. 

Tools—46-54-60-70-80-90-100-120-190. 
Vises—36-46-54-60-70-80-90. 
Wrenches—36-46-54-60-70-80-90-100- 
120 . 


185 


‘Courtesy of The Norton Company, 



THE 


STARRETT 


BOOK 


In other words, to maintain a satisfactory cutting speed 
slow the work revolution or increase the wheel speed if the 
grinding wheel acts too soft. If the wheel acts hard, increase 
the work revolution or decrease the wheel speed. If a wheel 
hums on small work, or roars a little on large work, it may 
be assumed that the wheel is cutting correctly. Wide faced 
wheels should usually be a little softer than narrow faced 
wheels for the same work. 

WHEEL DRESSING 

Truing or dressing a grinding wheel is not—or at least 
should not always be—done with the object of sharpening 
the wheel. The primary requisite for good grinding is a 
perfectly round, true wheel. The second requisite is a proper 
condition of the face of the wheel to accomplish the desired 
result on the work. Therefore, a wheel often should be 
dressed, not to “sharpen” it, but to true it up, and to put the 
wheel face in proper condition for the work, even though 
this means actually “dulling” rather than “sharpening” the 
wheel. 

In wheel dressing great pains should be taken to avoid 
scoring the wheel. For this reason, a diamond tool which 
has been used a short time is better for truing than a new 
diamond, because all the little sharp corners, projections, etc., 
have been worn off and the diamond maintains for a longer 
time the same area of exposed surface presented to the wheel. 

The speed with which the diamond is moved across the 
wheel is also a controlling factor in the work. Moving the 
diamond too rapidly across the wheel actually cuts a spiral 
or thread in the surface of the wheel and works havoc with 
the grinding finish. Such a wheel will invariably produce a 
mottled or frosted appearance on the surface of the work. 
The diamond should travel across the face of the wheel slowly 
enough to make sure that all the particles composing the 
surface of the wheel have been brought to the same height 
and are an equal distance from the center of the wheel. To 

186 



FOR MOTOR MACHINISTS 


do this, take light traversing cuts with the diamond tool. 
Allow plenty of water to flow on the diamond while truing. 

Be sure that the diamond is clamped rigidly in the tool 
holder on the table of the machine. The tool holder should 
be so set that a line running through its center and that of 
the diamond will strike the wheel surface at a downward 
angle of approximately 5° with a diameter of the wheel 
parallel to the plane of the table. This allows the diamond 
to wipe across the face of the wheel rather than dig into it, 
as would be done if the diamond pointed above the center of 
the wheel. 


LAPPING 

In certain lines of work the final grinding process is often 
made, not with abrasive wheels as previously described, but 
by using metal discs, rings, or cylinders, the surfaces of which 
have been charged with a fine flour abrasive. Such a tool is 
called a “lap”, and its use is known as “lapping”. Laps 
were first used by lapidaries in finishing the surfaces of min¬ 
eral specimens, but laps have been in common use for a 
considerable time on fine work in the machine shop. 

Laps are generally made of some material soft enough so 
that the abrasive can be readily pressed into the surface; or, 
as it is correctly termed, the surface is “charged”. Soft, 
close-grained cast iron, copper, brass, or lead may be used 
for the lap, and any of the flour abrasives may be charged 
into the surface by rolling the abrasive into the lap either 
with a hardened roll or on a hardened surface. 

In some of the finer grinding operations the lap is charged 
with diamond dust which has been precipitated or settled in 
a suitable dish of olive oil. The several grades are denoted 
by the time taken to precipitate; as, for example, fineness 
No. 5 takes ten hours. 

Since lapping is a somewhat slow and tedious process it 
should be used for the removal of extremely small amounts. 

187 



THE 


STARRETT 


BOOK 


GRINDING WHEELS FOR DIFFERENT MATERIALS 

The information below is intended to give an approximate idea of the grade used 
under ordinary conditions. 


Class of Work 


Alundum 

Grain 

Grade 

36 to 46 

3 to 4 Elas. 

20 

Q 

24 comb. 

J to K 

16 to 46 

H to K 

24 to 30 

P to R 

16 to 20 

Q to R 

20 to 30 

P to U 

36 to 60 

J toL 

20 to 30 

P to S 

30 

P to Q 

46 to 60 

J to M 

30 to 46 

J to K 

20 to 24 

PSil. 

20 to 36 

O to P 

20 to 36 

O to Q 

14 to 20* 

P to U* 

20 to 30* 

P to R* 

46 to 60 

I toM 

46 to 60 

J to M 

20 to 24 

P to Q 

46 to 60 

KtoO 

46 to 60 

J to M 

24 to 36 

J to M 

70 

l^to2Elas. 

30 to 50 

L to N 

60 

O to Q 

24 comb. 

L to P 

30 to 60 

L to O 

16 to 36 

H to K 

16 to 46 

H to K 

24 comb. 

K 

46 to 60 

J to L 

10 to 20 

Q to W 

20 to 30 

P to R 

16 to 46 

L to P 

46 to 60 

M 

36 to 60 

K toM 

12 to 30 

PtoU 

46 to 60 

K to M 


Crystolon or 
Carborundum 


Grain 


Grade 


Aluminum castings . 

Brass or bronze castings (large) ... 
Brass or bronze castings (small) 

Car wheels, chilled . 

Cast iron, cylindrical. 

Castings, iron (surfacing). 

Castings, iron (small). 

Castings, iron (large). 

Chilled iron castings. 

Dies, chilled iron... 

Dies, steel. 

Drop-forgings . 

Hammers, cast steel . 

Internal cylinder grinding. 

Internal grinding, hardened steel. .. 

Knives (planer) . 

Lathe and planer tools.j 

Machine shop use, general. 

Malleable iron castings (large). 

Malleable iron castings (small). 

Milling cutters, machine grinding. . . 

Milling cutters, hand grinding. 

Nickel castings. 

Pulleys, cast iron, surfacing faces of 
Reamers, taps, etc., hand grinding. . 
Reamers, taps, special machines. .. 

Rolls (cast iron), wet. 

Rolls (chilled iron), finishing. 

Rolls (chilled iron), roughing. 

Saws, gumming and sharpening. ... 
Saws, cold cutting-off. 

Steel (soft), cylindrical grinding. . { 

Steel (soft), surface grinding. 

Steel (hardened), surface grinding. . 
Steel (hardened), cylindrical f 

grinding. \ 

Steel, large castings. 

Steel, small castings. 

Steel (manganese), safe work. 

Twist drills, hand grinding. 

Twist drills, special machines. 

Wrought iron. 

Woodworking tools. 


20 to 24 
20 to 24 
24 to 36 
16 to 24 
30 to 46 
16 to 30 
20 to 30 
16 to 24 
16 to 30 
20 to 30 


30 to 60 


20 to 30 
16 to 20 


20 to 24 
30 to 36 


24 to 46 
70 to 80 
30 to 46 


PtoR 
Q to R 
P to R 
O to S 
I to L 
I to L 
Q to S 
Q to S 
Q to U 
O to Q 


I to L 


Q to S 
R to S 


R 

KtoL 


J to M 
lJ^to2Elas. 
2 to 5 Elas. 


* Annealed. 


Courtesy of The Norton Company. 


188 








































































































F 0 

R M 

[ 0 

TOR 

MAC 

H 

I N I S T S 

GRADES OF GRINDING WHEELS 

ARRANGED IN ORDER OF RELATIVE “HARDNESS” OR STRENGTH OF BOND 

Medium 

M N 

Ms Ns 

3E 4E 

y-p> \C*W 

CO -K 
CO 

SeoW 

CO 

N M L K 

6 5 4 

C3 D D1 D2 

<5^ 

00 

o ^ 

Z^-3 

CO 

z 

^ CO 

$ 

a< 

Dh 

^ VN 

Q. th\ 
^CO 

S 

eo\ 

CM 

V* 

r\C0 

CM 

rJW 

Wuo 

W 

rM rt< 

ooW 

r\ CO\ 

CO CM 

Medium 

Soft 

C/D „ 

hUW 

\c* 

CM 

C/3 

CM 

CM 

^cmW 

CM 

o» 

Dh oo 

Pi 

C f) 03 

h 

B2 B3 C Cl C2 

^oo 

\c* 

CM 

coW 

(N 

(N 

^Joo 

\cq 

m «n 

ffi 

0^ 

rH 

X 

% 

X 

s 

& 

£ 

c 

* : 
CM • 

CM • 

<N W 

Si 

poo 

w 

p^ 

W CM 

co W 

(JCM 

CM§ 

S/] Ph 

co w 

W 

CO 

Soft 

5 

MmH 

rH 

-jrW 

rH 

H 

W*- 

A3 B B1 

HH 

Mod 

-^cmIz; 

NjH 

t—4 eo\ 
rH 

E F 

1 

< 

< £ 

tH CM 

£ 

rH 

n w 

uw 

\cq 

rK 

\APi 

IN ^ 

W 

£ 

IN 

Very 

Soft 

C/D 

XXUi 

V 

co\ 

03 

oow 

\<N 

rK 

& 

0~\« 

>h2 

N 

CM 

< 

rH 

< 

< 

F G 

l IX 

rH 

rH 


9 

Z A\\ H 

l IX 

1 


<N 

Wo; 

CM CM 

Extra 

Soft 


E F 



D E 

IJH t-H P-, 


\N\(M 

*H\ r-t\ 

(JLO 

U CO 


• • 

• • 

• • 

• • 

• • 

w : 

& : 

rH 

W : 

^ : 

rH • 

Bond 

Vitrified 

Silicate 

Elastic 

Vitrified 

Silicate 

Elastic 

Vitrified and 
Silicate 
Elastic 

Vitrified and 
Silicate 

Vitrified and 
Silicate 
Elastic 

Vitrified 

Silicate 

Carborundum 

Vitrified and 
Silicate 
Elastic 

Vitrified 

Silicate 

Vitrified and 
Silicate 
Elastic 

Vitrified and 
Silicate 
Elastic 

Vitrified and 
Silicate 
Elastic 


Abrasive 

Company 

American Emery 

Wheel Works 

Carborundum 

Company 

Chicago Wheel and 
Mfg. Co. 

Detroit Grinding 
Wheel Company 

Landis Tool Co. 

Norton Company 

Safety Emery 

Wheel Company 

Sterling Grinding 
Wheel Company 

Vitrified Wheel 
Company 

Waltham Grinding 
Wheel Company 


189 










































































































Grades of Grinding Wheels—Continued 


THE STARRETT ROOK 


Extremely 

Hard 

N : : 

N • • 


t-H 

O 



Z A 

Q : 
• 

• 

\^i . 

oo\ • 

w : 

^ • 
rH\ 

u • 


o : 

P : 
X : 

lO . 

sd • 
3 : 

W : 
X : 

Extra 

Hard 

£ : : 

V w 





x : 

X 

w 

& 

z 

o • 

co ! 
fa . 

w : 

X : 
^ • 

• 

• 

• 

Very 

Hard 

• * 

p 

H 

I> 


F3 G 

S T 

u 

i-r 

F U 

£ : 

He* 

Z 

S 

z 

^ r-H 

o 

iO • 

• 

fH\ • 

Tt * 

. 

<n ; 

fa • 

« : 

X : 

■ 

Hard 

C/3 

. m * 

tf>M 

OOli 

wW 
PhPh co 

(y*o W 

w 

OrH 

E2 E3 F FI F2 

(X 

O»o 

0h*O 

CO 

C/)coE 

lO 

O* 

> 

Pt- 

h 

cno 

X 

O'M 

X 

o 

<N 

cox 

>-H 

iH\ 

HH 

eo\ 

co 

\N\W 

rH\Hv 

coco 

V* 

H\ 

CO 

rHfi] 

fa£ 

W 

CO 

fa co 

co 

Medium 

Hard 

e/)M 

ooS 

0h^ 

hH CO 

rH 

W 

W 

CO 

P 

z Af 

O N 


Pi 

<P*o 

Oh 

X 

HH 

HH CO 

X 

Oh 

coX 

CO 

aS 

iO 

^ . 

co\cO 

co 

Bond 

Vitrified 

Silicate 

Elastic 

Vitrified 

Silicate 

Elastic 

Vitrified and 
Silicate 
Elastic 

Vitrified and 
Silicate 

Vitrified and 
Silicate 
Elastic 

Vitrified 

Silicate 

Carborundum 

Vitrified and 
Silicate 
Elastic 

Vitrified 

Silicate 

Vitrified and 
Silicate 
Elastic 

Vitrified and 
Silicate 
Elastic 

Vitrified and 
Silicate 
Elastic 


Abrasive 

Company _ 

American Emery 
Wheel Works 

Carborundum 

Company 

Chicago Wheel and 
Mfg. Co. 

Detroit Grinding 
Wheel Company 

h— 1 - 

vo 

O Landis Tool Co. 

Norton Company 

Safety Emery 

Wheel Company 

Sterling Grinding 
Wheel Company 

Vitrified Wheel 
Company 

Waltham Grinding 
Wheel Company 


* Rubber Bond. 











































































































c$ 

PS 

• r-H 

43 

• rH 

IS 

43 

ph 


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g 

£ 

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hJ 

H-l 

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£5 

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Z 

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£ 

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192 















































FOR MOTOR MACHINISTS 


ANTI-FREEZING SOLUTIONS 

All Percentages are given by volume. 


DENATURED ALCOHOL SOLUTIONS 


Per Cent 
Water 

Per Cent 
Alcohol 

Specific 

Gravity 

Freezing 

Point 

Boiling 

Point 

100 

0 

1.000 

32 degrees 

212 degrees 

90 

10 

.987 

24 

200 

80 

20 

.975 

13 

185 

70 

30 

.964 

-2 

169 

60 

40 

.953 

-20 

163 

50 

50 

.934 

-34 

157 

40 

60 

.915 

-47 

152 

30 

70 

.870 

-57 

148 


WOOD ALCOHOL SOLUTIONS 


Per Cent 
Water 

Per Cent 
Alcohol 

Specific 

Gravity 

Freezing 

Point 

Boiling 

Point 

100 

0 

1.000 

32 degrees 

212 degrees 

90 

10 

.986 

20 

197 

80 

20 

.975 

8 

182 

70 

30 

.962 

-7 

166 

60 

40 

.949 

-24 

150 

50 

50 

.934 

-37 

134 

40 

60 

.917 

-52 


30 

70 

.850 

-60 



GLYCERINE SOLUTIONS 


Per Cent 
Water 

Per Cent 
Glycerine 

Freezing 

Point 

Boiling 

Point 

100 

0 

32 degrees 

212 degrees 

90 

10 

28 

215 

80 

20 

23 

218 

70 

30 

14 

222 

60 

40 

6 

224 

50 

50 

0 

227 

40 

60 

-3 

233 


WOOD ALCOHOL AND GLYCERINE SOLUTIONS 


Per Cent 
Water 

Per Cent 
Glycerine 

Per Cent 
Alcohol 

Freezing 

Point 

Boiling 

Point 

100 

0 

0 

32 degrees 

212 degrees 

90 

5 

5 

24 

204 

80 

10 

10 

15 

194 

70 

15 

15 

-5 

184 


CALCIUM CHLORIDE SOLUTIONS* 


Per Cent 
Water 

Per Cent 
Calcium Chloride 

Specific 

Gravity 

Freezing 

Point 

100 

0 

1.000 

32 degrees 

90 

10 

1.085 

22 

80 

20 

1. 179 

-1 

70 

30 


-60 


* The use of Calcium Chloride solutions is not recommended. 


193 




















































THE 


STARRETT 


BOOK 


HOW TO TELL CARBURETOR SIZES 


Carbureter 

Size 

Inside Diameter 
of Hole in Flange 

Carbureter 

Size 

Inside Diameter 
of Hole in Flange 

y 

u /6 


I'Wo 

Q/o 

'Wo 

m 

VWo 

% 

1 Wo 

2 

2 Wo 

Vs 

1 Wo 

2 ^ 

21 Wo* 

1 

1 Wo 

3 

3 Wo* 

1 H 

1 Wo 

3 H 

3>!4* 


* These sizes have four bolt holes, others have two. 


MAXIMUM POWER REQUIRED TO DRIVE MACHINE 

TOOLS 


12-in. lathe. 2 hp. 

14-in. lathe. 3 hp. 

16-in. lathe. 4 hp. 

18-in. lathe. 5 hp. 

20-in. lathe. 7 hp. 

22-in. lathe. 8 hp. 

24-in. lathe.9 hp. 

27-in. lathe.10 hp. 

30-in. lathe.11 hp. 

36-in. lathe.15 hp. 

24-in. drill press . 3W hp. 

60-in. planer .23 hp. 

42-in. planer .12 hp. 

42-in. mill .19 hp. 

H-in. sensitive drill. % hp. 

16-in. shaper. 2 hp. 

18-in. shaper. 3 hp. 

No. 1 Universal milling machine . 2 hp. 

No. 2 Universal milling machine. 2 hp. 

No. 3 Universal milling machine. 3 hp. 

6-in. grinding wheel (two wheels) . 1 hp. 

10-in. grinding wheel (two wheels). 2 hp. 

12-in. grinding wheel (two wheels). 3 hp. 

18-in. grinding wheel (two wheels). 7y hp. 


194 


































FOR MOTOR MACHINISTS 


WIRE AND SHEET METAL GAGES 


Gage 

No. 

Ameri¬ 
can or 
Brown 
& Sharpe 

Birming¬ 
ham or 
Stubbs 
iron wire 

Wash¬ 
burn & 
Moen 
iron wire 

U.S. Std. 
for plate 
(iron and 
steel) 

Stubbs 

steel 

wire 

Twist 
drill and 
steel 
wire 

Wash¬ 
burn & 
Moen 
music 
wire 

Wood 

and 

m’chine 
screw 

8-0 







.0083 


7-0 

• • 

.... 

.490 

.500 

.... 


.0087 


6-0 


.... 

.462 

.469 

.... 

.... 

.0095 


5-0 


.... 

.431 

.438 



.010 


4-0 

.460 

.454 

.394 

.406 


■ . • • 

.011 


3-0 

.410 

.425 

.363 

.375 



.012 

.032 

2-0 

.365 

.3S0 

.331 

.344 



.013 

.045 

0 

.325 

.340 

.307 

.313 


...» 

.014 

.058 

1 

.289 

.300 

.283 

.281 

.227 

.228 

.016 

.071 

2 

.258 

.284 

.263 

.266 

.219 

.221 

.017 

.084 

3 

.229 

.259 

.244 

.250 

.212 

.213 

.018 

.097 

4 

.204 

.238 

.225 

.234 

.207 

.209 

.019 

.110 

5 

.182 

.220 

.207 

.219 

.204 

.206 

.020 

.124 

6 

.162 

.203 

.192 

.203 

.201 

.204 

.022 

.137 

7 

.144 

.180 

.177 

.188 

.199 

.201 

.023 

.150 

8 

.128 

.165 

.162 

.172 

.197 

.199 

.024 

.163 

9 

.114 

.148 

.148 

.156 

.194 

.196 

.026 

.176 

10 

.102 

.134 

.135 

.141 

.191 

.194 

.027 

.189 

11 

.091 

.120 

.121 

.125 

.188 

.191 

.028 

.203 

12 

.081 

.109 

.106 

• .109 

.185 

.189 

.030 

.216 

13 

.072 

.095 

.092 

.094 

.182 

.185 

.031 

.229 

14 

.064 

.083 

.080 

.078 

.180 

.182 

.033 

.242 

15 

.057 

.072 

.072 

.070 

.178 

.180 

.035 

.255 

16 

.051 

.065 

.053 

.063 

.175 

.177 

.036 

.268 

17 

.045 

.058 

.054 

.056 

.172 

.173 

.038 

.282 

18 

.040 

.049 

.048 

.050 

.168 

.170 

.040 

.295 

19 

.036 

.042 

.041 

.044 

.164 

.166 

.041 

.308 

20 

.032 

.035 

.035 

.038 

.161 

.161 

.043 

.321 

21 

.028 

.032 

.032 

.034 

.157 

.159 

.046 

.334 

22 

.025 

.028 

.029 

.031 

.155 

.157 

.048 

.347 

23 

.023 

.025 

.026 

.028 

.153 

.154 

.051 

.360 

24 

.020 

.022 

.023 

.025 

.151 

.152 

.055 

.374 

25 

.018 

.020 

.020 

.022 

.148 

.150 

.059 

.387 

26 

.016 

.018 

.018 

.019 

.146 

.147 

.063 

.400 

27 

.0141 

.016 

.0173 

.0171 

.143 

.144 

.066 

.413 

28 

.0126 

.014 

.0162 

.0156 

.139 

.141 

.072 

.426 

29 

.0112 

.013 

.0150 

.0141 

.134 

.136 

.076 

.439 

30 

.0100 

.012 

.0140 

.0125 

.127 

.129 

.180 

.453 

31 

.0089 

.010 

.0132 

.0109 

.120 

.120 

• • • • 

.466 

32 

.0079 

.009 

.0128 

.0101 

.115 

.116 

. , . • 

.479 

33 

.0071 

.008 

.0118 

.0093 

.112 

.113 

• • • • 

.492 

34 

.0063 

.007 

.0104 

.0085 

.110 

.111 

• • • • 

.505 

35 

.0056 

.005 

.0095 

.0078 

.108 

.110 

. . . . 

.518 

36 

.0050 

.004 

.0090 

.0070 

.106 

.1065 

• • • • 

.532 

37 

.0044 



.0066 

.103 

.1040 

• • • • 

.545 

38 

.0039 



.0062 

.101 

.1015 

• • • • 

.558 

39 

.0035 




.099 

.0995 

, , , , 

.571 

40 

.0031 




.097 

.0980 


*■ .584 


195 



























THE 


STARRETT 


ROOK 


METAL REMOVED BY DRILLING 

Depth of drilling necessary to remove given weights when 
balancing machine parts, lightening pistons, etc. Inter¬ 
mediate weights may be found by adding together the depths 
of the holes corresponding to the different weights that go 
to make up the whole. The figure on the lowest line of the 
table is to be added in each case to the weight and the hole 
is measured at the side not at the center. 

BRASS 


Depth to Drill in Inches 


Weight 

Oz. 

One Inch 
Drill 

Three quarter 
Inch Drill 

One half 
Inch Drill 

Three eighths 
Inch Drill 

One quartei 
Inch Drill 

50 

40 

30 

20 

13.25 

10.60 

7.95 

5.30 

18.86 

14.16 

9.44 

21.22 


. 

10 

2.65 

4.72 

10.60 

18.86 


9 

2.38 

4.24 

9.54 

16.97 


8 

2.12 

3.77 

8.48 

15.08 


7 

1.85 

3.30 

7.42 

13.20 


6 

1.59 

2.83 

6.36 

11.31 

25.46 

8 

1.32 

2.36 

5.30 

9.43 

21.22 

4 

1.06 

1.88 

4.24 

7.54 

16.96 

3 

.79 

1.41 

3.18 

5.65 

12.72 

2 

.53 

.94 

2.12 

3.77 

8.48 

1 

.26 

.47 

1.06 

1.88 

4.24 

.9 

.24 

.42 

.95 

1.69 

3.81 

.8 

.21 

.37 

.85 

1.52 

3.39 

.7 

.18 

.33 

.74 

1.33 

2.96 

.6 

.16 

.28 

.63 

1.14 

2.54 

.9 

.13 

.23 

.53 

.95 

2.12 

.4 

.11 

.19 

.43 

.76 

1.69 

.3 

.08 

.14 

.31 

.57 

1.27 

.2 

.05 

.09 

.21 

.38 

.85 

.1 

.02 

.05 

.11 

.19 

.42 

Deduct for 






point of 
drill 

.10 

.075 

.05 

.04 

.03 


196 



























FOR MOTOR MACHINISTS 


STEEL 


Weight 

One Inch 

Three quarter 

One half 

Three eighths 

One quarter 

Oz. 

Drill 

Inch Drill 

Inch Drill 

Inch Drill 

Inch Drill 

50 

14.19 

25.26 




40 

11 .36 

20.20 




30 

8 52 

15.16 




20 

5 68 

10.06 

22.73 



10 

2.83 

5.05 

11.38 

20.21 


9 

2.55 

4.55 

10.23 

18.18 


8 

2.27 

4.04 

9.08 

16.16 

36.37 

7 

1.98 

3.54 

7.96 

14.14 

31.83 

6 

1.71 

3.04 

6.82 

12.12 

27.28 

3 

1.41 

2.54 

5.68 

10.10 

22.73 

4 

1.14 

2.01 

4.55 

8.08 

18.18 

3 

.85 

1.51 

3.41 

6.06 

13.63 

2 

.57 

1.01 

2.28 

4.04 

9.08 

1 

.28 

.50 

1.14 

2.02 

4.55 

.9 

.26 

.45 

1.02 

1.83 

4.08 

.8 

.22 

.40 

.91 

1.62 

3.64 

.7 

.19 

.35 

.79 

1.40 

3.17 

.6 

.17 

.30 

.67 

1.22 

2.72 

.5 

.14 

.25 

.57 

1.01 

2.28 

.4 

.11 

.20 

.45 

.81 

1.83 

.3 

.09 

.15 

.33 

.61 

1.37 

.2 

.06 

.10 

.22 

.41 

.91 

.1 

02 

.05 

.11 

.20 

.45 

Deduct for 






point of drill 

.10 

.075 

.05 

.04 

.03 



CAST 

IRON 



50 

15.43 

27 50 




40 

12.36 

22^00 




30 

9.27 

16.50 




90 

6 19 

10^94 

24.75 



10 

3i08 

5i47 

12.38 

22.02 

. 

9 

2.78 

4.95 

11.12 

19.81 

. 

8 

2.47 

4.40 

9.90 

17.60 

39.60 

7 

2.16 

3.86 

8.66 

15.41 

34.65 

6 

1.86 

3.31 

7.43 

13.20 

29.72 

5 

1.54 

2.75 

6.18 

11.00 

24.75 

4 ' 

1.24 

2.20 

4.96 

8.80 

19.80 

3 

.93 

1.65 

3.71 

6.60 

14.85 

2 

.62 

1.09 

2.48 

4.40 

9.90 

1 

.31 

.55 

1.24 

2.20 

4.96 

.9 

.28 

.49 

1.11 

1.98 

4.34 

.8 

.25 

.44 

.99 

1.76 

3.96 

.7 

.22 

.39 

.87 

1.54 

3.46 

.6 

.19 

.33 

.74 

1.32 

2.97 

.5 

.15 

.28 

.62 

1.10 

2.48 

.4 

.12 

.22 

.50 

.88 

1.98 

.3 

.09 

.17 

.37 

.66 

1.49 

.2 

.06 

.11 

.25 

.44 

.99 

.1 

.03 

.06 

.12 

.22 

.50 

Deduct for 






point of drill 

.10 

.075 

.05 

.04 

.03 


197 











































THE 


STARRETT 


BOOK 


INSTALLING FLYWHEEL RING GEARS* 

Motor repair shops today are frequently called on to re¬ 
place damaged flywheel, or starter, ring gears. If the gear 
ring is of steel, shrunk onto the cast-iron flywheel, the job 
is comparatively simple, it being necessary only to remove 
the old ring by sawing or drilling it, and shrink on a replace¬ 
ment ring. When, however, the gear teeth are cut in the 
body of the cast-iron flywheel, the work is considerably more 
difficult. 

To replace a damaged flywheel ring gear, the teeth of 
which are cut in the body of the wheel, the following method 
should be followed: Mount the damaged flywheel in a lathe 
or boring mill so that it may be turned down to take the new 
ring. The chief difficulty in this part of the operation is cen¬ 
tering the wheel and if the chalk method is used in truing 
up or centering the work, the job may well take several hours. 
To center the wheel quickly, place it in the chuck on a pipe 
center held in the tail stock of the lathe, and use an ampli¬ 
fying dial gage to indicate how much the wheel is running 
out of true. The pipe center itself centers the flywheel within 
a few thousandths of an inch and the work may easily be ad¬ 
justed so it runs perfectly true by means of the chuck jaws. 

In the turning operation the old teeth are removed, the 
tool being fed in from the side with a broad cut so that it 
works below the base of the gear teeth, avoiding vibration 
and chatter. When turned down to size the wheel is ready 
for shrinking on the ring gear. 

Before shrinking the new ring gear into place it must be 
expanded by heating, in either a regular rim heating forge, 
or other suitable furnace, or by means of several blow torches 
if neither of the other means are available. The ring should 
be heated to a blue heat and care should be taken to heat all 
parts of it equally. When heated to the proper degree, the 
ring is removed from the furnace and quickly slipped over 
the rim of the flywheel. The contraction of the ring gear 

* Data on Allowances for Shrink Fits may be found on pp. 15 and 17, Vol. II, 
Starrett Books. 


198 



FOR MOT OR MACHINISTS 


as it cools will be sufficient to lock it firmly in place on the 
rim of the flywheel. To estimate the allowance for a good 
shrink fit the following formula may be used: 


A = allowance in thousandths of an inch 
D = nominal diameter of fit 


A 

1000 


= JL D -{- 5" 
16 D + * 5 


DEFINITIONS OF ELECTRICAL TERMS 

Alternating Current —(Abbrev. ac)—An electric current 
which alternately reverses its direction around a circuit, as 
distinguished from a direct current (dc) in which the current 
flows in one direction only. The process of changing an 
alternating current to a direct current is called rectification 
and is accomplished by an apparatus known as a rectifier. 

Ampere —the unit of measurement of electric current. The 
current which is produced by the electrical pressure, or E M F, 
of 1 volt applied to a conductor the resistance of which is 
1 ohm. 

Ampere Hour —the quantity of electricity transferred by a 
current of 1 ampere flowing for one hour, or its equivalent; 
such as four amperes flowing for fifteen minutes. 

Capacity —the quantity of electricity in ampere hours which 
may be taken from a cell or storage battery at a given rate 
of discharge. 

Circuit —Conductors connected with a source of electrical 
supply are collectively called a circuit. When they form a 
closed path through which a current circulates there is a 
closed circuit; when there is no closed path and no current 
circulates, there is an open circuit. 

Continuous Rating —denotes the load which the electrical 
machine can carry continuously without overheating or 
deterioration. 


199 




THE STARRETT BOOK 


E M F —electromotive force—that force which causes or 
tends to cause an electric current. 

Frequency —the number of complete periods of alteration 
per second of an alternating current. 

Kilowatt Hour —(abbrev. kw.-hr.)—the unit commonly used 
in measuring electrical energy. The energy represented by 
1 kw. operating for one hour or its equivalent, i. e., 3 kw. 
operating for 20 minutes. 

Ohm —the unit of resistance. The resistance requiring an 
E. M. F. of 1 volt to maintain a steady current of 1 ampere. 

Parallel Circuit —a circuit in which the parts of the circuit 
are connected in independent circuits branching from the 
main circuit. Also known as a shunt circuit. 

Polarization —When a cell is generating current the metal 
dissolved from the positive plate combines with the liquid in 
the cell to form hydrogen gas which appears in the form of 
bubbles on the surface of the negative plate, diminishing the 
amount of surface in contact with the liquid and so increasing 
resistance and reducing current. The hydrogen bubbles are 
positive and set up an opposing E. M. F. which further re¬ 
duces the current. 

Rating—Normal Rating denotes the load which a motor or 
generator or transformer is designed to carry under service 
conditions. 

Series Circuit —A circuit in which the several parts are 
connected so that the same current passes through all. Thus 
cells are in series when the positive of one is connected with 
the negative of another. 

Volt —The unit of measurement of electromotive force. 
The E. M. F. required to send a steady current of 1 ampere 
against a resistance of 1 ohm. 

Watt —The electrical unit of power. 1 horsepower equals 
746 watts or .746 kilowatts. 


’ 200 



FOR MOTOR MACHINISTS 


DEFINITION OF SYMBOLS USED ON 
WIRING DIAGRAMS 


+ 

Positive side of battery or 
electrical circuit. 

1 — 

Negative side of battery or 
electrical circuit. 

! ip= 

Indicates battery, either stor¬ 
age or dry cells. 

i— 

Indicates a grounded connec¬ 
tion. 


45)- 

Indicates a dome or instrument 
board light. 

—- 

Indicates direction of current 
flow (mostly used on internal 
diagrams). 

c.w. 

Indicates clockwise rotation. 


Indicates counter-clockwise 
rotation. 

OR 

C.C.tY. 

-W\AAr 

Indicates a coil of heavy wire 
(primary circuit of ignition 
coil). 

•AAAMr 

Indicates a coil of light wire 
(secondary circuit of igni¬ 
tion coil). 

o 

Indicates a shunt wound 
generator. 

01 

Indicates a series wound 
generator. 

+ 

Indicates a connection between 
wires. 

— 

Indicates crossed wires not 
connected. 

-\aJv~ 

Indicates a rheostat or vari¬ 
able resistance. 


Indicates a push button or 
light switch. 




Indicates a starting switch. 


© 

© 


II—II 


-d?~ 

PI — 

A/V 

o 


-0- 


ItfPil 


© 

QMf 

-vwwvw- 

-wvwvwv 


Indicates a three terminal 
motor-generator. 


Indicates a four terminal 
motor-generator. 


Indicates an automatic cut-out. 


Indicates location of fuse in 
circuit. 


Indicates heavy cables (start¬ 
ing circuit wiring). 


Indicates a condenser. 


Either symbol indicates the 
breaker points of an ignition 
system. 

Indicates a resistance such as 
a resistance unit and charg¬ 
ing resistance. 


Indicates a movable brush and 
brush lifting switch. 


Indicates. #< A M Ammeter and 
"V” voltmeter. 


Indicates a push button switch. 


Indicates a single-throw switch. 


Indicates the distributor of 
an ignition system. 


Indicates motor of a single 
unit system. 


Indicates generator of a sin* 
gle unit system. 


Indicates a ballast coil. 


Indicates a compound wound 
coil, primary circuit shown 
in heavy lines and secondary 
in light lines. 


Courtesy 


of American Automobile Digest. 


201 























































THE 


STARRETT 


ROOK 


A TOOL FOR EVERY JOB* 

To operate at a profit it is essential that the shop be well 
equipped. While the following items by no means constitute 
everything a well-found shop should have, they may be of 
assistance in checking up needed equipment. 


Hand Tools 
Hammers 

1 Blacksmith’s 

2 Blacksmith’s Sledge, short handle 
Blacksmith’s Sledge, long handle 

2 Machinist’s Ball Pein 

1 Machinist’s Straight Pein 
1 Rawhide Mallet 
1 Lead or Babbitt Headed Hammer 

Wrenches 

*1 Socket Wrench Set, with ratchet 
handle, No. 443 

3 Stillson Wrenches, 6", 12", 18" 
3 Monkey Wrenches, 6", 12", 18" 

1 set Double End S Wrenches 

1 complete set Spanner Wrenches 
1 Bicycle Wrench, 4" 

1 Narrow Jaw Monkey Wrench, 8" 

2 Adjustable End Wrenches, 6", 8" 
Set of Magneto Wrenches 

*1 Small Hand Vise, No. 200 

* Tap Wrench, No. 93-C 
Pliers etc. 

2 Combination Pliers, 6", 10" 

* Cut Nipper Pliers, No. 1 

Side cutting, parallel jaw Pliers 
Special anti-skid chain Pliers 
Cotter Pin Pliers 
Piston Ring Expanding Pliers 
Tinner’s Snips 
Heavy Shears 
Bolt Cutter 
Screw Drivers 

‘ * Set Magneto Screw Drivers, 
No. 555 

3 Screw Drivers, 6"xJ4", 10"x^", 

12"x>£" 

Files 

Bastard, 10", round, square, and 
three cornered 

Second Cut, 8", flat, half round 
Finishing Cut, 8", flat, half 
round, rat tail, three cornered 
Finishing Cut, 6", rat tail 
Set of File Handles 
File Brush 

Small and large Oil Stones 
♦Indicates Starrett Tools with Catalog 


Chisels 

Cape, small, medium, large 
Chipping, small, medium, large 
RoundNose,small,medium,large 
Diamond Point, small, medium, 
large 

Bench Equipment 
Pipe Vise 

2 Swivel Vise, medium and large 
Surface Plate 
Bench Anvil 

* Machinist’s Clamps, No. 278 

C Clamps, large, medium and 
small 

Angle Bender 

* Bench Block, No. 129 
Miscellaneous 

Movable and Wall Benches 
Wheeled Trucks and Jacks 
Oil and Gasoline Storage Facili¬ 
ties 

Water Heater 

Washing Stand and Equipment 
Light Stand 

Small Blacksmith’s or Brazing 
Forge, complete 
Anvil (500 lbs.) and Block 
Fire Extinguishing Equipment 

Measuring Tools 
♦Machinist’s Try-Squares, 6", No. 55 
♦Carpenter’s Try-Squares, 24", No. 451 
*Combination Square ana Protractor, 
No. 9 

♦Machinist’s Flexible Scales, 2", 6", 
12", No. 320 

♦Machinist’s Stainless Steel Rule, 6", 
No. 1000 

♦Steel Tape, 50 ft., No. 512 
♦Steel Shrink Rule, No. 374 
♦Tempered Steel Rules, with Holder, 
No. 423 

♦Carpenter’s 2-ft. Folding Rule, No. 451 
♦Spirit Level with Cross Level, No. 134 
♦Micrometers 

♦Outside, l", 2", 3" and 6", Nos. 
436 224 

♦Inside, 2" to 8", No. 124 
♦Screw Thread, No. 575 


202 



FOR MO TOR MACHINISTS 


Measuring Tools— Continued 
*Gages 

Taper, No. 269 
Thread, Nos. 29, 40, 155, 473 
♦Center, No. 390 
Thickness, No. 71 
♦Cylinder, No. 452 
♦Vernier Height with Attachment, 
No. 454 

♦Vernier Depth, No. 448 
Tap and Drill, No. 185 
♦Drill Point, No. 22 
♦Surface, No. 257 
Telescope, No. 229 
♦Micrometer Depth, No. 440 
♦Calipers 

♦Pocket Slide, No. 425 
♦Hermaphrodite, small, medium, 
No. 243 

♦Inside Lock Joint, small, medium, 
No. 37 

♦Outside Lock Joint, smal 1, medium, 
No. 36 

♦Vernier, No. 122 
Machine Tools 

Valve Grinding Machine 
Piston Grinding Machine 
Cylinder Grinder 

Lathe—preferably a Gap Lathe, and 
two or more in the following sizes: 
10", 14", 18", 24". If but one is 
installed, it should be the 24" size. 
Shaper, 16" stroke 
Universal Miller 
Bench Drill 
Sensitive Drill Press 
Vertical Drill Press, heavy 
Radial Drill Press 
Arbor Press 
Hack Saw Machine 

Miscellaneous Tools 

Service Car, equipped with wrecking 
crane, chain hoists and own set of 
hand tools 

Portable Shop Crane 

Wheel Puller 

Gear Puller 

Breast Drill, 2 speeds 

Electric Drill 

Gasoline Blow Torch 

Set of Number Drills 

2 Sets of Taps and Dies, S. A. E. 

Standard, and U. S. Standard 
2 Jack Screws 
Bending Bars 


Pneumatic Hammer and Riveter 
Air Compressor for Tool Operation 
Welding Table 

Oxy-Acetylene Welding Torch and 
Tanks complete with Welding 
Tools and Rods 
Carbon Burning Outfit 
Radiator Work Bench, Tank and 
Tools 

Overhead Trolley Tracks fitted with 
chain hoists 
Auto-Turn 

Motor and Rear Axle Stand 
Piston Aligner 

Miscellaneous Hand Tools 
Valve Spring Lifters 
Valve Seat Reamers 
Complete set Critchley Type Expan¬ 
sion Reamers, to l 15 /f 6 " 
Complete set Critchley Type Align¬ 
ing Reamers with Pilots 
Hand Drill, 1 speed 
Belt Punch 

Bit Brace with Ratchet and complete 
set of Bits 

Carpenter’s Cross-Cut Saw 
*2 Hacksaw Frames No. 169-144 and 
Blades (See Starrett Hacksaw 
Chart) 

♦Slotting Saw, No. 249 
♦Ratchet Drill Set, No. 443 
Spring Winder 
Chassis Spring Spreader 
Carbon Scrapers 
Bearing Scrapers 
Jack Plane 

Wood Chisels, x /i" to 2" 

♦Center Punches, No. 264 
♦Drive Pin Punches, !4" to 
point, Nos. 565 and 248 
Soldering Irons 

♦Spring Dividers, small, medium, 
No. 277 

♦Universal Dial Test Indicator, No. 
196 

♦Hand Vise, No. 86 
♦Decimal Equivalent Tables, Nos. 
589, 590, 591 

Tap and Drill Gage Tables, No. 185 
♦Drill Blocks, No. 271 
Toolmakers’ Steel Clamps, Nos. 161, 
160 

♦Bevel Protractor, No. 490 
♦Protractor, No. 364 
♦Center Tester, No. 65 
♦Set of Scribers, No. 67 


Indicates Starrett Tools with Catalog Number. 

203 




THE 


STARRETT 


BOOK 


ASSORTMENTS OF DRILLS FOR 
TAPPING 


Assortments include both tap and body drills. 

No. 1—For National Fine and Coarse Threads,* No. 0 to 1 inch, 50 drills: 

2, 3, 8, 11, 15, 17, 19, 21, 26, 28, 29, 30, 33, 36, 38, 39, 42, 44, 

46, 49, 50, 51, 52, 53, 56, A, % %, 2 Vi, % Vs, 2 Vi, 2 Vi, As, 

2 Vo 8 Vi, % % As, 3 Vi, 21 A, "As, a A, 4 Vo Vs, 'As, 1- 

No. 2—For National Coarse Threads, No. 1 to 1 inch, 23 drills: 

2, 8, 11, 17, 19, 26, 28, 29, 30, 33, 36, 39, 44, 47, 49, 51, 53, A, 

As, 2 Vi, 2 Vi, As, 3 Vo A, % As, 5 A, 2 Vi, a A , 4 Vo Vs, l. 

No. 3—For National Fine Threads, No. 0 to 1 inch, 39 drills: 

2, 3, 11, 15, 19, 21, 28, 29, 30, 33, 38, 39, 42, 44, 46, 49, 50, 52, 

53, 56, V. 'A, As, 2 Vi, 3 A, 2 Vi, As, 2 Vi, 3^, 3 Vi, As, *Vi, "Ve, 

M, % 15 d«, I- 

No. 4—For National Fine and Coarse Threads, No. 6 to A inch, 33 drills: 

2, 3, 8, 11, 15, 17, 19, 21, 26, 28, 29, 30, 33, A, 'A, As, 2 Vi, % 

2 Vo 2 Vo As, 2 Vi. 3 Vi, 3^, 3 Vi, 17 Vs, Ve, % 2 A, "As, H-. 

No. 5—For National Fine and Coarse Threads, No. 6 to As inch, 27 drills: 
2, 3, 8, 11, 15, 17,' 19, 21, 26, 28, 29, 33, 36, A, 'A, As, 2 Vo 2 Vo 
A, 2 A, 2 Vo Vo 2 Vi, 3 Vi, A, 3 A, As- 


No. 6—For National Coarse Threads, No. 6 to As inch, 18 drills: 

2, 8, 11, 17, 19, 26, 28, 29, 36, A. As, 2 Vi, A, 2 Vi, As, 3 Vo A, As- 


No. 7—For National Fine Threads, No. 6 to As inch, 20 drills: 

2, 3, 11, 15, 19, 21, 28, 29, 33, A, "A, As, 2 Vi, A, 2 A, As, 2 Vi, 
A, 3 Vi, As- 

No. 8—For Pipe Threads, A inch to % inch, 5 drills: 

2 Vo 2 Vi, As, 'As, 2 A- 

No. 9—For Standard Taper Pins, No. 00 to No. 6, 8 drills: 

32, 29, 27, 21, 15, 4, A, %- 

N->. 10—For Cotter Pins, As to *Vi inch, 7 drills: 

2, 11, 21, 28, 30, 36, 48. 

No. 11—For Wood Screws, No. 4 to No. 18, 38 drills: 

2, 3, 4, 6, 8, 12, 14, 16, 17, 19, 20, 23, 24, 25, 26, 28, 30, 31, 32, 

33, 35, 38, 40, 42, 44, 45, 48, 49,51, 52, % A, 'A, A, 'Vi- 


No. 12—For General Automobile Shop use. Includes all body and tap 
drills necessary for National Fine and Coarse Threads, No. 6 to As inch. 
Pipe Threads A to A inch. Standard Taper Pins, No. 00 to No. 6, Cotter 
Pins As 1° *Vi inch. Wood Screws, No. 4 to No. 18, 50 drills: 


2, 3, 4, 8, 11, 12, 14, 15, 16, 17, 19, 20, 21, 23, 24, 25, 
28, 29, 30, 31, 32, 33, 36, 38, 40, 42, 44, 45, 48, 49, 51, 52, 
V, As, "A, 2 Vi> 2 Vi> Vs, 2 Vi, 2 Vi, As, 2 Vo 3 Vi, 8 Vi, As- 

*See pages 85,97 and 98. 


26, 

A, 


27, 

17 Vi, 


204 



FOR MOTOR MACHINISTS 


CHAIN DISCOUNTS 

Many automobile accessories, etc., are sold to the trade 
subject to what are known as chain discounts and which 
frequently are not only difficult to figure, but actually mis¬ 
leading. The following table is, therefore, submitted. To 
use it, multiply the list price by the figure in the extreme 
right-hand column that corresponds to the chain discount 
given. For example: A given article or part costs $12.00 
less a chain discount of 25%+ 10%+ 5%. This discount is 
found in the seventh line from the top of the table, and, 
according to the figures under “Total Discount”, is equiva¬ 
lent to .35875. To find the net cost of the goods, multiply 
the list price by 100 less .35875 or . 64125, the figure given in 
the right-hand column. 


Chain Discounts 

Total Disc. 

Multiply by 

25% = . 

.25 

.75 

25% 4- 5% = . 

.2875 

.7125 

25% 4- 5% 4 5% =. 

.32312 

.67688 

25% 4- 5% 4 5% 4 5%= . 

.35697 

.64303 

25% 4 10% = . 

.325 

.675 

25% 4 10% 4 10% =. 

.3925 

.6075 

40 /Q “ 2.KJ /Q | AV//0 . 

.35875 

.64125 

05 % -l. 10% 4 5% 4 5% = . 

.39081 

.60919 

25% 4- 10% 4 5% 4 5% 4 5% = . 

.42127 

.57873 

20 % = . 

.20 

.80 

20 % 4 5% = . 

.24 

.76 

20 % 4 5% 4 5% =... 

.278 

.722 


.3141 

.6859 

4\) /o iT /0 o/Q X^ **/O . 

2ft% 4 - 10% = . 

.28 

.72 

20% 4 - 10% 4- 10% = . 

.352 

.648 

4\J /Q ±\J/Q X /V . 

90% 4- 10% 4 5% =. 

.316 

.684 

4\J /q x 1 /O i u /O . 

20 % 4 - 10% 4 5% 4 5% = . 

.3502 

.6498 

4U /o /O \ /o \ /q . 

20 % 4 - 10% 4 5% 4 5% 4 5% = . 

.38269 

.61731 

4\J /q ~r xyj /0 * u /Q i ** /0 \ /Q . 

— . 

.15 

.85 

x ° /o . 

1 ZOY K07- — . 

.1925 

.8075 

10/0 T u /0 . 

i cor 4 - 5% 4- 5% =. 

.23287 

.76713 

AO/0 ° /0 ~ u '0 . 

1KC/ 4- 5% 4- 5% 4- 5% =. . . 

.27123 

.72877 

AO 70 | O /q "x o /o t o /o . 

15% 4 10% = . 

.235 

.765 


205 


































THE 


STARRETT 


ROOK 


Chain Discounts—Continued 


Chain Discounts 

Total Disc. 

Multiply by 

15% + 10% + 10% =. 

.3115 

.6885 

15% + 10% + 5% =. 

.27325 

.72675 

15% + 10% + 5% + 5% = . 

.30959 

.69041 

15% + 10% + 5% + 5% +5% = . 

.34411 

.65589 

10% = . 

. 10 

.90 

10% + 10% = . 

.19 

.81 

10% + 5% — . 

.145 

.855 

10% + 5% + 5% =. 

.18775 

.81225 

10% + 5% + 5% + 5% = . 

.22836 

.77164 

5% = . 

.05 


5% + 5% — . 

.0975 

.9025 

5% + 5% + 5% —. 

.14262 

.85738 

5% + 5% + 5% + 5% = . 

.18549 

.81451 

33H% = . 

.3333 

.6667 

33^% +5% = . 

.3667 

.6333 

33^% + 5% + 5% =. 

.3984 

.6016 

33^% + 5% + 5% + 5% = .. 

.4283 

.5717 

33M% + 10% = . 

.40 

.60 

33X% + 10% + 10% =. 

.46 

.54 

33K% + 10% + 5% =. 

.43 

.57 

33M% + 10% + 5% + 5% = . 

.4585 

.5415 

33H% + 10% + 5% + 5% + 5% = . 

.48557 

.51443 

50% = . 

50 


50% + 5% = . 

.525 

.475 

50% + 5% + 5% =. 

.54875 

.45125 

50% + 5% + 5% + 5% = . 

.57131 

.42869 

50% + 10% = . 

.55 

.45 

50% + 10% + 10% =. 

.595 

.405 

50% + 10% +5% =. 

.5725 

.4275 

50% + 10% + 5% + 5% = . 

.59387 

.40613 

50% + 10% + 5% + 5% + 5% = . 

.61418 

.38582 

60% = . 

60 

AH 

60% + 5% = . 

.62 

.38 

60% + 10 % = . 

.64 

.36 

60% + 10% +5% =. 

.658 

.342 

70% = . 

70 


70% + 5% = . 

.715 

. oU 

.285 

70% + 10% = . 

.73 

.27 

70% + 10% + 5% =. 

.7435 

.2565 


206 



















































INDEX 


ACETYLENE Torch, Use of 
Acme Thread, Formulae 
Annular Ball Bearings 

Tables of Equivalent . 

Anti-Freezing Solutions, Formulae for 
Arbors ..... 

BALANCING Motor Parts, by Drilling 
Ball Bearings. Annular 

Tables of Equivalent 
BEARINGS, Burning-in 

—Connecting Rod, Fitting 
—Crankshaft. Fitting 
—Main Truing 
—Scraping . 

Brazing .... 

Breaker Points, Contact, Setting 
Burning-in Bearings 

CALIPERS, Hermaphrodite 
—Micrometer 
—Micrometer Thread 
—Outside Thread 
—Toolmakers* 

—Vernier 
Caliper Squares . 

Carburetor Sizes . 

Center Gage 

Chain Discounts, Figuring 
Change Gears for Lathe, Placing 

—Selecting 

Chipping .... 

Chucking .... 

Cold Chisels, Grinding . 

Combination Set 
Compounding Gears for Lathe 
Contact Breaker Points, Setting 
Continuous Drill Table 
Counterboring 
Cutting Compounds 
Cutting Speeds and Feeds for Turning Tools 
CYLINDERS, Grinding 
—Honing 
—Lapping 

CYLINDER Bores, Gaging 

—Measuring with Inside 
Micrometer 

DECARBONIZING . 

Decimal Equivalents, Fractions of an Inch 
Definitions of Electrical Terms 
Dial Gages 
Dial Test Indicator 
DIES 

—Adjustable 
—Die Stock 
—Rethreading 
—Sharpening 
—Solid 

—Spring Threading 
—Use and Care of 
Discounts, Figuring Chain 
DRILLING 

—Cutting Compounds for 
—Deep Holes 
—for Reaming 
—for Tapping 
—Holding the Work 
—Large Holes 
—Metal Removed by 
—Speeds and Feeds 


20' 


134,135 
93 

191, 192 

193 

150 

196,197 

191,192 
120,121 
116-120 
116-121 
118 
119 

132 
100 

120,121 

141 

11 

156 

156 

6 

10 

9 

194 
137 

205,206 
152-154 

151 
129,130 
164, 165 
130, 131 

6 

155 
100 
69 
64 
53 
163 
107-110 
110,111 
110 
103 

19 

133 
22 

199. 200 

20 
24 

80- 83 
82 
81 
81 
83 
81 
82 
83 

205, 206 
45- 64 
53 
64 
62 
63 
57 
36 

196, 197 
58- 62 













INDEX 


—Starting 









56 

—to Balance Motor Parts 








196,197 

DRILL Assortments for Tapping 

• 








204 

—Points, Form of 









47- 52 

—Press 









59 

—Sizes for Taps 









66- 70 

—Shanks, Types of 









46 

DRILLS for Reaming . 









43 

—Grinding 









51- 63 

—Parts of . 









45, 46 

—Twist, Letter Size . 









66 

—Twist, Numbered Sizes 









65 

—Twist, Using . 









57- 60 

ECCENTRIC Turning 
ELECTRICAL Terms 




• 





162-164 

Definitions of 









199, 200 

“FEEL” .... 









8 

FILES, Cuts 









26 

—Handling 









27 

—Parts of . 









27 

—Shapes of 









25 

—Using 









24, 28, 29 

FITTING Connecting Rod Bearings 








116-120 

—Crankshaft Bearings 









116-121 

—Pistons . 









112, 113 

—Piston Pins 









115, 116 

—Piston Rings . 









113,114 

—Valves . 









121-124 

Fits and Fitting 









112-126 

Flat Work, Tools for 









7 

Flywheel Ring Gears, Installing 









198, 199 

GAGES, Center . 









137 

—Cylinder 









103-105 

—Dial 









20 

—Telescoping . 









106 

—Sheet Metal . 









195 

—Wire 









195 

Gear Meshing 









103 

GRINDING 









178-190 

—Amount to Leave for 









181 

—Cold Chisel 









130,131 

—Controlling Speed of Cutting 








184,185 

—Cylinders 









107- 110 

—Cylindrical 









181 

—Flat Surfaces . 









184 

—Grain Numbers 









185 

—Lapping. 









187 

—Measuring 









183, 184 

—Mounting the Wheel 









183 

—Roughing for . 









181 

—Selecting Wheel 









182 

GRINDING Wheels . 









178-190 

—Abrasive 









179 

—Bonding 









180 

—Combination . 









179 

—Comparative Grades of 









189-190 

—Dressing 









186 

—Elastic . 









179 

—Grading 









180 

—Silicate . 









179 

—for Various Materials 









188 

—Vitrified 









179 

HACKSAWS, Blade Recommendations 








33 

—Use of . 









29- 32 

Hermaphrodite Calipers 









141 

Honing Cylinders 









110- 111 

KEY WAYS, Milling . 









170-174 

Knurling 








• 

166 

LAPPING, Cylinders 









110 

—Crank Ping 





• 




117 


208 














INDEX 

-—— ---^ 


—Grinding 
—on Lathe 
LATHES . 

—Adjusting 
—Care of . 

—Compound- Gears 
—Indicating 
—Locating Centers 
—Work, Measuring 
—Placing Change Gears 
—Selecting Change Gears 
—Thread Cutting 
—Work Centers 
LATHE Tools . 

—Arbors . 

—Clearance for 
—Cutting Angles for 
—Cutting, Materials for 
—Grinding 
—Mandrels 
—Rake of . 

—Setting . 

—Tool Holders 
—Uses of . 

LAYING Out, General 

—for Drilling 
—Locating Centers for Drilling 
—Preparing the Surface 
Lead Burning .... 

MACHINE Tools, Power Required to Drive 
Mandrels . 

Materials, Grinding Wheels for 
Measuring Lathe Work 
Measuring Tools, General 
Metal Removed by Drilling . 

Metric Thread Formulae 
MICROMETER Calipers 
—Adjustment of 
—How to Read 
—Inside 
—Parts of . 

—Phantom View of Outside 
Micrometer Depth Gage 
MILLING 

—Cutters, Teeth in 
—Keyways 
—Machine Parts 
—Splines 

NATIONAL Coarse Thread Series 
—Fine Thread Series 

PISTON, Fitting 

—Pins, Fitting 
—Rings, Fitting 
Protractors, Use of 

REAMERS 

—Drills for 
—Sharpening 
—Taper 
—Taper Pin 
—Types of 
—Uses of . 

Round Work, Tools for 

SCRAPING Bearings . 

SCREW Threads 
—Acme 
—Double . 

—Fits . . - _ . 

—Measuring and Testing on Lathe 
—Metric . 

—National Coarse Series 
—National Fine Series 


187 
166 

135 - 167 
136 

136 - 138 
155 
138 
141 

155 - 157 
152-154 
151 
151-155 
141 

143 - 150 
150 
144 

148 
149 . 150 
147,148 

150 
143 
146,147 

149 

144 - 146 
126,127 

53 - 55 

54 

55 
133 

194 

150 

188 
155-157 

5 - 21 
196 , 197 

91 

11 - 20 
17 , 18 
13 , 14 
18 - 20 
13 
12 
6 

167-176 
171 
170-174 
169 
175 , 176 

97 

98 

112.113 
115 . 116 

113.114 
127 

34 - 44 

43 

40 - 42 

44 
43 

34 - 36 
36 - 40 
7 

119 
84 - 98 

92 
87 
71 

155 

91 

97 

98 


209 

















INDEX 


—Parts of . 

—Standards 
—Triple 

—U. S. Standard 

_“V” 

—Whitworth 

Screws, Wood, Specifications 
Shapers 

Sheet Metal Gages 
Shim Fitting 
Shop Equipment 
Soldering 

Spark Plug Gaps, Setting 
Splines, Milling . 

Square Thread Standard 
Standard Keyways for Milling Cutt 
Standard Taper Pins . 

TAP and Body Drills . 

TAP Drills 

—Pipe Thread . 

—S. A. E. Standard 
—Sizes, Comparison of 
—S. A. E. Threads 
—75 per cent Depth Thread 
—Stove Bolt Threads 
—U. S. S. Threads 
—Whitworth Threads 
TAPER Pin Reamers 

—B. & S. Sockets for 
—Jar no 
—Morse 
Taper Turning 

■—Without Taper Attachmen 
Tapers, Rules for Figuring 
—Table of 
Tappets, Adj usting 
TAPS 

—Parts of 
—Regrinding 
•—Removing Broken 
—Types of 
—Using 

Thickness Gages, How to Use 
—Uses for 
Test Indicator 
Thread Cutting, Lathe 
Tools for Every Job 
—Lathe 

Truing Main Bearings . 
TURNING, Eccentric 
—Taper 
—Tools, Cutting Speeds and 
U. S. Standard Thread Formulae 
—Thread Table . 


ers 


Feeds for 


VALVES, Fitting . . • . 

—Grinding-in .... 

—Refacing .... 
Valve Stems, Straightening . 

“V»> Thread, Formulae .... 
VERNIER Capipers .... 

—Height Gage 
•—How to Read 

Vernier Micrometer .... 

WELDING. 

Whitworth Thread Formulae. 

Wire Gages ..... 
Wiring Symbols, Definitions of 
Woodruff Keys, Cutters for . 

—Sizes ..... 

Wood Screw Specifications . 

Wrench Sizes for Bolts, Nuts and Cap Screws 


210 


86 , 87 

85 . 86 
88 

89 
88 

91 

76 

176 , 177 
195 
102 
202-204 
132 
100 
175 , 176 

92 
171 

43 

74 

66 - 75 

75 
73 
68 
71 

94 , 95 

75 

70 , 71 

71 

43 

44 
44 
44 

157 - 162 

158 - 160 
162 
161 
101 

77 - 80 
79 

78 , 79 

79 , 80 

77 

78 

99 , 100 
100-103 
139 
151-155 
202-204 
143-150 
118 
162 - 164 
157-162 
163 

90 
96 

121-124 
123 
122 
122 
88 
10 
11 
14 
16 
131 

91 
195 
201 
173 

172-173 

76 
23 














THE STARRETT BOOK 

FOR MACHINISTS* APPRENTICES 

Price 75 Cents 

Digest of Contents of Vol. I of The Starrett Books 


ABRASIVES, Grain of 
Algebra, Elementary 
Equations 

Algebraic Coefficients 
Signs 

Aligning Shafting 
Angle, Measurement of 

BELTS, Lengths, Formulae for 
Bench Work 

CALIPERS, Hermaphrodite 
Inside 
Micrometer 
Outside 
Spring 

Testing Screw Threads 
Verniers 
Carbon Steel 
Drills, Speed of 
Change Gears 
Chipping 
Chisels for 

CHUCKING 
Tools lor 

Contact Measuring 
Counterboring 
Cup Wheels 
Cutters, Milling 
Grinding 

Compounds for Drills 
Lips of Drills 
Screw Threads 

Thread, Compound Gears for 

DIVIDERS, Spring 
Drawings, Abbreviations for 
Detail 

DRILLING 
Deep Hole 
Holding Work 
Large Holes 
Laying Out for 
for Reaming 
Starting Drill 
for Tapping 

Torri nlpfq 

Drills, Cutting Compound 
Cutting Lips 
Drawing 
Kinds 

Letters, Sizes of 
Making 
Speed 
Testing 

EMERY, Grades of 
Engineering Formulae 
Equations 


Equivalent Tables 
Exponents 

FILES, Kinds 
Filing 
Draw 

Testing Surface 
FITS, Amounts to Leave 
Forced 

Fittings, Flanged 
Forces 

Formulae, Shop and Engineering 

GEARS, Compound, for Thread Cutting 
Speed of 
Thread Cutting 
Trains 

Gear Speeds, Formulae for 
Grades of Emery 

GRINDING 
Allowances for 
Amounts to Leave 
Cylindrical 
Flat Surfaces 
Measuring Work 
Milling Cutters 
Speeds for 

Wheels, Grade and Grain 
Wheels, Grading 
Mounting 

HACK SAWS 
Choice of 
Cutting Speeds 
Machines 

INVOLUTES 

JIGS, Boring Holes in — Body 
Bushings 

for Drilling Cylinder Flange 

and Fixtures 

Types 

KNURLING 

LAPPING 

Lathes 

Centers 

Gearing 

Grinding 

Setting 

Tools 

Lathe Work, Measuring 
Laying Out, for Drilling 
Plate for 

Preparing Surface for 
Scribing for 




211 





Digest of Contents of Vol. I of The Starrett Books 


Leveling Instrument, How to Set Up 

Levers 

Limits 

Lubricants 

MANDRELS, Use of 
Measuring Lathe Work 
Screw Thread 
Tools 

Work, Grinding 
Mechanics 
Mensuration 
Metals, Expansion of 
Melting Point of 

MICROMETER, Adjusting Buttons with 
Adjustment for Wear 
As a Gage 
Calipers 
How to Read 
Quick Adjustment 
Screw Thread 
Milling, Cutters 
Milling Cutters, Grinding 

PLANE FIGURES 

Polishing 

Pulleys 

Pulleys, Diameter, Speeds. Formulae for 

REAMERS, Making 

SCREW THREAD 
Measuring 
Pitch 

Properties of U. S. S. 

Section Lines 
Shafting, Aligning 
Leveling 
Shop Formulae 
Specific Gravity of Gases 
Liquids 
Metals 
Substances 


Heat of Substances 
Stellite 

TABLES, Allowances for Different Classes 
of Fits 
Grinding 

Brown & Sharpe Taper Shank 
Composition of Alloys 
Grinding Wheel Speeds 
Letter Sizes of Drills 
Morse Taper Shanks 
Sizes of Tap Drills 
Speeds and Feeds for Drilling 
Specific Gravity of Gases 
Liquids 

and Properties of Metals 
of Substances 

Tap Drills A. S. M. E. Standard 
Machine Screws 
Tapers 

Templets for Drilling 
U. S. S. Screw Threads 
Tap Drills, Sizes of 

TAPER in Given Length 
Shanks 
Testing 
Turning 

Offset of Centers 
Targets 
Thread Tools 
Tolerance, Limits 

TOOL MAKING 

Turning, Eccentric 
Work Centers 

VERNIER, How to Read 
Micrometer, How to Read 

WORK CENTERS, Locating 


212 



THE STARRETT DATA BOOK 

Price 75 Cents 

Digest of Contents of Volume II of The Starrett Books 


ABRASIVES 
Acme and Square Threads 
Alloys, Composition of 
American Wire Gage 
Angles and Tapers 
Angles Corresponding to Taper 
Annealing, Steel 
Angles lor Cutting Spirals 
Arbors, Keyways for 
A. S. M. E. Standard Screws 
Standard Threads 
Automatic Screw Machine Tools 
Tempering Temperatures 

BELTING 

Birmingham Wire Gage 
Boring 

Box Tools, Finish, Speeds and Feeds 
Turning, Cutting Speeds and Feeds 
Brass, Cutting Speed for Milling 

Screw Stock, Speeds and Feeds for 
Cutting 

Sheets, Rods, Bars, Weight of 
Tubing, Thickness 
Weights of 
Briggs’s Formula 
Standard Pipe Taps 
Taper Pipe Threads 
British Association Screw Threads 
Standard Whitworth Pipe Thread 
Brown & Sharpe Standard Taper Sockets 
Taper Shanks 
CASTINGS, Shrinkage of 
Change Gears for Cutting Spirals 
Chords, Length of, for spacing off circum¬ 
ferences of circles 

Chrome Nickel Steel, Cutting Speed for 
Milling 

Cutting Tools, External, Surface Speeds, 
Time of Travel 

DECIMAL EQUIVALENTS 
Fractions 
of an inch 
millimeter 
Dies, Speeds for 
DRILLS, Carbon Steel 
Feeds and Speeds 
High Speed Steel 
Sizes 

Tap, sizes 
Twist, dimensions 
Wire Gage sizes 
Drilling, Lubricants 
Speeds and Feeds 

FEEDS, Cutting, Box fuming Tools 
Hollow Mills 

Roughing Brass Screw Stock 
Roughing Cold Rolled Stock 
for Drills 

Finish Box Tool 
Forming 
Reaming 
Screw Machine 


FITS, Driving 
Forcing 
Push 
Running 
Shrinking 

Tolerances and Allowances 
Forming, Feeds and Speeds 

Gages, Table of Limits for Limit 
GEARS, Blanks Turning and Cutting 
Change for Cutting Spirals 
Diametral, Metric, and Circular Pitches 
Internal Spur 

Spur.Circular Pitch,Rules and Formulae 
Spur, Diametral Pitch, Rules and 
Formulae 

Teeth, Metric or Module System 
Tooth Parts 
Gear Cutters, Bevel 
Offset 
Set-over 

Carbon Steel, Feed for 
High Speed Steel, Feed for 
Involute 

Comparative Curves 
Gear Cutting, Feeds 
Geometric Problems 
Grinding 

HACK SAW, Cuts per hour 
Speeds 
Selection of 

Heat, Treatment High Speed Steel 
High Temperatures, Colors of 
Holes, Standard, Tolerances 
Horsepower, Transmission of 
IMPERIAL WIRE GAGE 
Inches and Sixteenths in Millimeters 
Index, Milling Standard Table 
Iron, Cast, Cutting Speed for Milling 
Selecting by Spark Method 

JARNO TAPERS 

Standard Taper Sockets 
Reamers for 

KEYS, Barth 
Dimensions of 
Heads, Proportions 
Square, Feather Sizes 
Straight, dimensions of 
Sunk, proportions of 
U. S. Navy Standard 
Whitney, Cutters Nos. 

Dimensions 
Key-Seats, dimensions 
Size of cutter for 
Keyways, Standard Arbors 
for Cutters 

Knurls, Tempering Temperatures 

LAYING OUT 
Lathe Tools, Cooling Medium 
Grinding 
Hardening Heat 


213 



Digest of Contents of Vol. II of The Starrett Books 


Leads for Cutting Spirals 
Lubricants, Chucking 
Cutting 
Drilling 
Reaming 
Tapping 
Turning 

MACHINE SCREWS, A. S. M. E. 
Standard Taps for 
A. S. M. E. Special Taps for 
Taps, dimensions 
Steel, Cutting Speed for Milling 
Materials, Average Ultimate Strength of 
Grinding Wheels for 
Metals, Average Ultimate Strength of 
Common Modulus of Elasticity 
Linear Expansion 
Melting Point 
Specific Gravity 
Metric, Conversion Tables 
Standard Screw Threads 
MILLING, Cutting Spirals 
Standard Index Table 
Milling Cutters, Cooling Medium 
Cutting Speeds 
Grinding Clearances 
Hardening Heat 
Number of Teeth in 
Standard Key ways for 
Temper 
Tempering 

Mills, Face, Cutting Speeds 
Hollow, Cutting Speeds 
Spiral, Cutting Speeds 
Morse Standard Taper Shanks 

PIPES, Standard, Briggs’s formula 
Taps, Briggs’s Standard 
Threads 

Wrought, dimensions 
weight 

Planer, time of travel per foot 
feet of travel per hour 
Tools, cooling medium 
grinding 
hardening heat 
Planing, Cutting Speeds for 
PRECISION MEASUREMENTS 
Pulleys, Circumferential Speeds of 

REAMING, Lubricants 
Feeds and Speeds 
Reamers, Clearances 
Taper 

Reed Tapers 

S. A. E. SCREWS, Standard, dimensions 
Threads 
Tolerances 

SCREWS AND THREADS 
Screw and Nut Tolerances 
Close fits 
Loose fits 
Medium fits 

Screw Machines, clearances for threading 
Feed per revolution 

Screw Threads, Adapting Lathe to cut 
Metric 

British Assoc. Drills for 
Constants for finding diameter at 
bottom 

Double depth of 
Metric Standard 
Pitch, V, U. S., Whitworth 
S. A. E., Tap Drill Sizes 


Table of diameters and corresponding 
pitch 

Tolerances 
U. S. Standard 
Whitworth 

Sellers Hobs, dimensions 
Tapers 
SHAFTING 

Special Machine Screws, Top Drills for 
Speeds and Feeds for Finish Box Tool 
Box Turning Tool 
Face Mills 
Hollow Mills 
Milling Cutters 
Roughing Brass Screw Stock 
Cold Rolled Stock 
Spiral Mills 
Turning Tools 
Dies 
Drills 
Forming 
Reaming 
Screw Machines 
Taps 

Threading 

Squares, Cube Roots, etc., of fractions 
Distance across corners of 
Rules relative to 

Square and Acme Threads, Comparison 
Square Thread Taps 
Standard Pipe and Pipe Threads 
Steam Pipe dimensions 
weight 

STEEL, Carbon, percentageof, in toolsteel 
Temper of 
Tools adapted to 
Cast, Average Ultimate Strength 
Weight 

Flat-Bar, weight 
Forging Heat 

Heat Treatment, of High Speed 
Plates, weight 

Plow, average ultimate strength 
Selecting by Spark Method 
Structural 

Tool, Cutting Speed for Milling 
Wire, diameter of 
Strength of 

TAPERS, amount of 
and angles 

Brown & Sharpe taper shanks 
Jar no 

Morse Standard 

Per foot and corresponding angles 

Reamers and Pins 

Reed 

Rules for Figuring 
Sellers 

Tap Drills for Machine Screws 

Sizes for S.A.E. Standard Screw Threads 
TAPS, A.S.M.E. Special Machine Screws 
Standard 

Briggs’s Standard Pipe 
Cooling Medium 
Die, dimensions 
Hand, dimensions 
Hardening Heat 
Machine Screw, dimensions 
Pipe, drill sizes for 
Speed for 
Square Thread 
Stove Bolt 
Tapper, dimensions 
Temper 


214 




Digest of Contents of Vol. II of The Starrett Books 


Tempering Temperatures 
Tapped Hole Limits 
Tapper Taps 
Tapping, Lubricants 

Tempering, Color of High Temperatures 
Temperatures for Tool 
Thread Dies, Tempering Temperatures 
Threads and Screws—A.S.M.E. Standard 
Clearance between top and bottom of 
Sizes of Drills 
Size of Taps 
Parts, Tables of 

Threading, Screw Machine Clearance 
Surface Speeds for 
TOLERANCES, Driving Fits 
Forced Fits 
* Push Fits 
Running Fits 

Screw and Nut for Close Fit 


Loose Fit 
Medium Fit 
Screw Threads 
Standard Holes 
TURNING AND BORING 
and Cutting, Gear Blanks 
Tools, Cutting Feeds and Speeds 

U. S. STANDARD Screw Thread 

Washburn & Moen Wire Gage 
Water Pipe, dimensions 
Weights and Measures 
Whitworth Standard Thread 
Micrometer Readings 
Wire, Copper, area circular mils 
Length ft. per ohm 
Resistance, ohms 
per 1,000 ft. 


215 










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